You can buy all the stuff to rebuild your stock starter from the parts store--brushes, bushings, and the solenoid. You can also get the bendix/gear on the end of it. I rebuilt mine in that fashion and it works great. Where it is a pain is installing it--you can't put it in with the manifold on the car--it has to be installed simultaneously with the manifold.
My guess is the mini starter you bought was made to be used with the manifolds that go on the Lesabre/Wildcat/Electra--they are alot more plentiful.