[OCMDGTO]

3.55 to 3.36 will be hardly noticeable. 3.23 to 3.50 in my car was only a 150rpm difference

[geeteeohguy]

Originally Posted by OCMDGTO

3.55 to 3.36 will be hardly noticeable. 3.23 to 3.50 in my car was only a 150rpm difference

I swapped the 3.55 rear gear in my 4 speed '65 GTO for a set of 3.36 gears in 1990. My cruise speed went from 60 mph to 70 mph. To me, a big enough difference to be worth it.

For the OP: with the Muncie M-20 and the 428, I would source a 3.08 geared rear end and bolt it in and be done with it. Thousands cheaper than a 5 speed conversion, you get to keep your 4 speed and Hurst shifter, and the swap can be done in a day with no modifications other than changing the speedometer gear at the tailhousing.