Dick, order paperwork a bit tough for me to read. But option descriptions can be deceiving.
For example, the mandatory additional equipment with the 3.90 gears shows the "Speedo Adaptor" as you pointed out. However, you may not be aware, but with 4 spd., no speedo adaptor was ever used. A specific wide ratio trans, p/n 9774826 was used since it was assembled with the internal 6 tooth speedo drive gear. Without 3.90 gears tranny p/n 9774825 was used with the 8 tooth speedo drive gear.
The 3.90 gears were available in almost all A bodies, including certain 6 cyl applications where a standard brake peg leg could be used. For the 4 bbl 326, 4 bbl 389, and T-P cars, however, the only 3.90 axle available was the code 3P which was strictly Safe-T-Track with Metallic Brakes.
A 4 bbl 326 or 4 bbl 389 would not have automatically gotten the HD Radiator, so the addition of the HD Rad when 3.90 gears were ordered would be at extra cost. However, the Tri-Power already required the HD Rad at extra cost. Adding the 3.90 axle to a Tri-Power car still "required" the HD Rad, but it was the same Rad and same added cost as was already going to be reflected on the Invoice and Window Sticker, so no actual change.
As to the Fan, I am not aware of a running change in '64 affecting the GTO fan and fan clutch. AFAIK, the original std. GTO fan was 7 blade, 18" dia. and p/n 9775582 with Clutch p/n 9775578 exc. with A/C. This fan & clutch was not used for any other '64 factory application that I am aware of.
Same fan was used for the T-P GTO.
For the GTO with A/C or special equipment option Sales Code 644 Heavy Duty Fan, a 7 blade 19.5" dia. Fan p/n 9775580 with Clutch p/n 9775579 was specified. This Fan & Clutch was used for all A body with V8 & A/C. However, it was NOT the HD Fan for the 326 applications.
You mention the straight vs. curved tips and unpainted vs. painted blades. I am unfamiliar with those distinctions.
Although the Clutch p/ns did not change and the Clutch itself was separately serviced, the Service Replacement p/ns for the GTO Fans became 9777013 for the 19.5" dia. and 9777014 for the 18" dia. I do not know why these p/ns changed from what I know of the factory installed p/ns except that perhaps Pontiac did not service these Fans except as an assembly with the Clutch installed. I cannot imagine another explanation for why the Fan p/n itself would have changed. I do not think there was a running change affecting the factory fan p/ns during '64.
I do not know of the existence of an even "heavier" duty Fan or Clutch that may have been used when the close ratio trans was specified.
Having looked at a few original T-P GTO Window Stickers, I suspect that the HD Rad was always listed separately as an "automatic" extra cost line item whenever T-P was ordered. In other words, you didn't have to check it off in the order, but you would get it anyway and it would be priced separately from the T-P option. Same when you ordered 3.90 axle, with or without T-P, HD Rad was listed separately as a line item. That doesn't explain the one very late built T-P GTO that lists the regular GTO Rad code 50 on the Manifest (no Window Sticker to check), but it generally explains why HD Rad would be priced separately from any other option on the Window Sticker. That way, you never paid for it twice, even though it was required with two different options (T-P & 3.90 axle).
That would also explain why the car with the close ratio trans shows the HD Fan at extra cost on the Window Sticker. The T-P GTO did not get the bigger Fan unless it could be special ordered (see below) or if the car got A/C.
With close ratio, the bigger Fan was mandatory, so it was listed as a line item.
A/C was not available with the 3.90 axle and V8. You could order the code P 3.90 axle with Man Trans 4 bbl 326, any 4 bbl 389, or any T-P. You got the bigger Rad with any of these but no shroud. But if you ordered the close ratio trans, you had to take a lot of other stuff, including the HD Fan (and maybe a shroud, see below).
So if you wanted to improve the cooling efficiency of any GTO, you could do what 3 Deuce 64 did and add a shroud. And if you did not have the 2.63" thick Rad, you could swap to that. And you could also add the bigger Fan.
Incidentally, you could add A/C as a Dealer Accessory Package. From what I can tell, the field installation included adding the 18" clutched Fan that was standard in the GTO. It also included a specific shroud and seals set-up, shroud sized for the smaller Fan as compared to the Factory A/C set-up. Since the GTO already had the same Fan as was to be installed with the Package, I'm not sure what was done with the Fan that may have been in the Package but I don't think there was a GTO specific A/C Package, so the GTO Owner was cheated a bit, I suspect, while the 326 Owner got a new Fan installed. The reason the Package did not use the 19.5" dia. Fan was because the 326 applications had the shorter Rad. It might have made sense to have a GTO specific A/C Dealer Package that would have included the bigger Fan & Shroud, but Pontiac apparently didn't elect to offer that, perhaps because there would have been very little demand.
Dick, I'm not sure about the terms 4 core & 3 core. But I think this relates to the 2.63" thick and 2" thick GTO Rads. So based on what I think is true, the Tri-Power was specified with the HD 2.63" thick Rad (I am aware of at least one late year exception) but the standard 18" clutched Fan. The shroud was only added with A/C (I believe with trailering options also), and was not available as a separate factory option. The HD Fan was required with the late year close ratio trans option. The HD Fan was a special equipment option, Sales Code 644 on the All Series Special Equipment Order Form.
There is one caveat to this latter claim. In '65, the HD Fan was not offered as a separate option for the GTO. It still was required with the close ratio trans option.
It occurs to me that Pontiac may not have wanted to offer the 19.5" dia. Fan in a GTO without the shroud, so they simply did not allow the HD Fan available as a separate option with the GTO. Very possibly, when the close ratio trans was ordered, you were required to order the HD Rad & HD Fan and what you got was the same Rad set-up and Fan as you would have gotten with A/C; shroud, seals, and all. Perhaps Pontiac thought it was a bit unsafe to have that large Fan not surrounded by a shroud, but with close ratio trans treated it same as if A/C or a trailering option had been ordered.
If so, then you will never see the HD Fan option on a '64 GTO unless it was optioned with the close ratio trans. In fact, as I think about it, this makes the most sense from the evidence I have seen.
It would be pretty easy to improve the cooling efficiency of any GTO by making use of the components from any '64 V8 with A/C.
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