[olddog]

As one who has the .64 and hates it with a passion, I will make two points. The 4th to 5th shift is really like shifting from 4th to 6th. I had 3.50 rear gears and when I rebuilt the rear end I tossed in a set of 3.89 gears. 1-4 was perfect with the 3.50 gears, but 5th was too tall to go under 70 mph. Now with the 3.89 4th is too low to talk over. If you have very much cam you will learn to hate it. A BB with a mild cam will run OK.

Point two. If you really need the .64 then look at a 6 speed transmission. You will be happier.