Magnum 318 info

You just need a trans for the block series.
A /6 needs an/6 trans.
A small block needs a small block trans.
A big block needs a big block trans.

After that, the trans spline count is different if it is really old. My ‘67 Cuda has an odd spline count. Stupid hard to find a performance converter for it. I had a local shop down the block from me open it up and restall it.
(https://protorque.com/)