1971 La318 Starter issue?

Hello all. So I've got a 1966 Dart GT Convertible with a 1971 318 in it that I am looking to do a bit of work to over the winter. (Something along the lines of a 318WillRun style build). I figured I should do some compression tests to make sure the engine was a good candidate without needing a complete rebuild, since if that's the case, I'd rather not spend the money on a 318, but work on a 340 or 360 instead. That's all beside the point for the moment though. I pulled the plugs, unhooked the coil wire, and went to turn the engine over to start checking compression. The engine turned over once, then the starter just whined. It kept doing this. I thought it was maybe a battery not being charged up enough, but even when charged it kept happening. If I turned the motor over by hand, I heard an immediate click that sounded like the starter wheel disengaging. I discovered that if I kept the key turned, it would turn over once, whine for 3-4 seconds, then turn over again, then whine for 3-4 seconds, turn over, etc. etc. So the question is, is it a starter issue? It seems odd to me that it would turn over again while holding the key to 'start' if it was the starter sticking. Does anyone have any experience with this issue? If it is the starter, I believe I read that you can use a newer truck magnum starter on these?

Thanks!
I would have to hear it. Mopar starters when they are good and the battery is fully charged will go Wing ding, ding, ding If yours doesn't spin over like this one you have issues.