[sdbob]

If I wanted long term reliability 4spd, I check out Paul Cangailosi (spl) 4speeds. I spend $$ upfront to get convenience, not working on it. Just my 2cts.

[Sirrotica]

Troy beat me to the light..........

Since GM already made the Dearborn 3 speed adaptable by drilling both case patterns into the bellhousing, the Ford top loader 4 speed can be switched into the GM car with minimal adapting. Lots more strength in one of the top loader 4 speeds than any Muncie or Borg Warner transmission, but that strength comes with a weight penalty, The Ford offering is much heavier duty from the get go.

As far as early/late Muncies strength I would speak from experience that the 73 Grand Am 4 speed I owned was a much better strength wise than any of the earlier 64-72 Muncie equipped cars I owned. With mostly stock 389s and 400 engines, and street tires myself and friends trashed dozens of early Muncies.

The 73-74 Muncie equipped transmissions were designated as M20 HD had a fine splined input shaft same as the M 22 and the same output shaft size as a T400 has. Not exactly easy to locate used ones as they only were installed for 2 model years.

Pontiac didn't offer the Muncies in and 455 A body cars 73-74, only 400 cars. The engineers must have calculated that sidestepping the clutch on a 2 plus ton car with a 455 wasn't going to get through the warranty period.

Going from memory the 64-65 Muncies had a smaller diameter cluster gear shaft, and in 1966 it was increased I believe 1/8th of an inch to aid in deflection.

If I were looking to do this swap myself I'd likely try to get a later BW from some car such as a Trans Am. Other than main shaft roller bearings needing replaced under 50,000 miles they're usually trouble free, and are superior to early BW transmissions as far as strength. In the 70s when I owned my garage the only problems I saw on the late BW was the roller bearings wearing prematurely, causing whine while driving. Cure was to replace the roller bearings and you were back in business.

For brute strength in an older transmission the Ford top loader would win.

I have zero experience with the late model stuff, or the after market 5-6 speeds. so I can't comment.

Myself if I wanted 4 forward gears behind a 455 it will be a 4L80E and bonus of .75 OD in 4th, likely it will outlast the engine with no broken parts, but it can be expensive depending upon how you attack the conversion.