For repairing the starter on a RAM 500 I used the ElectriFly T-370 6.0-9.6volt. I think it gives a little more RPM than the 280 but not sure. If your bendix is held on by set screw and you need a slip fit I reduced the dia. of the spline using a Dremel cut off wheel. I hooked the motor to a battery to spin fairly slow and then very lightly applied the cutoff wheel to the splined motor shaft. The motor and the Dremel need to be held very securely so the smallest amount is removed. The dia. of the shaft will reduce fairly quickly, don't go too far.

Most any dealer can order the motor from Great Plains if they don't have it in stock. Dealers that specialize in model cars will be more likely to have it.