'50 Chevy starter engaging with engine running

I'm building a '50 Fleetline with 216. When I start it up the starter sounds like it's bumping against the flywheel or trying to engage. It doesn't do this at idle and not all the time.when it does it the ammeter dps hard This is a project car so it's not been on the road yet. I've installed a different engine and tranny from a doner car as a unit ( the old one was toast), new wiring harness and switches except starter button, also had the starter rebuilt. Would the problem be the the button or the starter too close to the flywheel? I've sprayed electrical parts cleaner in the button and no change nor do I get feedback when not running ie. starter engaging when button not pushed. Sorry so long winded, but trying to give pertinent info. Thanks for any tips

 

Maybe you could scab in a toggle switch and start the car cut the toggle off and see if the starter still acted up. If so it would be the bendix I would think that maybe had a broken are weak spring. You could disconnect the button and use a remote starter . Probably the easiest way.

 

1950. And the starter and solenoid are the ones from the same engine. Engine, tranny, front suspension, torque tube, rearend and suspension were all swapped as a unit from a driver that was being moderized.

 

Thanks 325w, sounds like a reasonable plan of attack.