68 slant six trans to 64 225 slant six

The earlier trans will likely be cable shift, the 68 trans will not. You didn't mention what car/year it was going into.
jus sayin....
As stated. The trans will bolt up to the engine, but the converter is a mismatch. The trans will not be a "bolt in" into a 65 or older "A" body. Different shifter, speedometer cable connection, different driveshaft hookup.