Big Block and Small Block Bells are different.
There are also 10.5 and 11" clutch versions of the Big Block Bells, which means different flywheels.
There are also Internal and External Balance Flywheels.

The transmissions are specific to Body. A, B or C. Unsure of truck but van has a unique mounting. Shifter location was standard on B Bodies.

Driveshafts before 65 Had a Ball and Trunion Mount vs. 65 and later Sip Yoke.

If you are drag racing you may be required to run a blowproof Bell.