[KS circutguy]

Pretty interesting, don't know if this is a re post.
But really worth a watch.
Does plumbing the rear of both Pontiac Heads help the engine's temperature? Only if it's plumbed correctly! Check out why it works... It'll blow your mind, and not your head gasket. In addition, I also show you the Correct way to install AN fittings.

In this episode, "Pontiac Head Cooling Trick - Part 2 Keeping Your Heads Cool" I'll diagram the Pontiac Water Flow, and what I did to help it... or, did I hurt it? We shall see! Enjoy!

https://www.youtube.com/watch?v=v_qUY4E33r0

[Formulabruce]

Do you just like plumbing?,There is a right way to cool the engine.. ZERO plumbing needed.. I'm surprised Monty didn't do this, he had his engine apart so many times..
Do the 421 mod WITH the 3 block plugs, Add the center cooling hole to Block and head using the gasket as template, then.. END of story and look and is stock..
This mod forces coolant Back in the block before it goes into the intake, and cools the center ports. This Evens out the engine temps at all cylinders.
Pontiac Stopped drilling the center hole for a good reason. On all cars except southern ones, they simply took longer than desired for warm up.

[KS circutguy]

His version you don't have to pull heads or motor.
I do get your point though.

[Formulabruce]

One thing of note: Back in 57-59 when Pontiac engines showed up in GMC trucks they used the older style cooling which put external hoses to these long tubes that went inside the heads from the front . These tubs had holes in them to release cooler water. The tubes had Bigger holes at the rear than the front to help even out temps and prevent water from short cutting to the T stat.