Lets start from scratch, are you having problems with that style starter?

Is it cranking really slow or some other issue?

If it is, cranking slow, simply replacing it with a new or fresh rebuilt one may cure the problem.

Later model starters simply crank faster that the old gear reduction did.

What you have isn't the typical gear reduction Mopar starter.

It's more like a Chevy in some respects with the solenoid on top of the starter.
They used that style starter on 66 & 67 Hemi's with a 4 speed and some slant sixes back then.