this is a handy tool . it has many popular trans. in calculator
https://www.tremec.com/calculadora.php
modern trans , have a much lower 1st gear set than old 4 speeds and auto. keep that in mind .
i always tried to match the gear so rolling through the 1/4 engine would be at max rpm. with that and a O.D. trans you could match you gear set to running through 1/4 in 4th . that would let you have 5 or 6th for highway
I have a Z06 with a 6 speed . I really dont like 6th gear much it just kills the power