Best gears for a /6 ??

What size tires?Are you still running 13s?Or short 14s like 25.5 tall?
Then 3.23s and that 3.09 make a nice 9.98 starter gear, that cruises at 65=2768; Not so bad for the straight six.

FWIW
I peglegged a 7.25 behind a 340 and 904 for about 2 years. The tranny gave up first.
But not just any 340. This hi-compression one had all the 2bbl teener top end, and cam, and with fenderwell headers. So basically it was big-bore teener. Torque? You better believe it.