Please tell me what parts interchange between the 2.45/2.25 vice 2.71->up 8 1/4 axle

I recently procured an 8 1/4 axle housing w/ 2:76 for my 65 Barracuda upgrade. Mild 318 & 904: 95 % around town driving + 26" tires. Came across a set of 3:55 gears out of a 83 pickup. Considering fun versus pragmatism. I have read about lock up torque converters that lower rpm ~200? RPM.
Is this available for a 65 tranny? Also have a 74 904 also, dunno if linkage/peripherals in 65 make 74 tranny possible.

A lock up torque converter has some gear-ratio effect..