I am currently running a 3.50 gear in my 66 with a Tremec (5th is same as T-5).
This is a nice gear for either a lot of freeway driving or a mellow motor.
I plan to get a set of 4.11s very soon as my setup isn't exactly mellow. 3.73s are a great gear too, probadly the best for your setup
------------------
|