Odd starter problem, pleade help quick!

Even if the flexplate were bent (unlikely), I think the torque converter can go back only ~1/4" before it bottoms out in the tranny. At least that is the gap I remember when installing a transmission, before pulling the torque converter to the flexplate. The starter teeth should well overlap the ring gear when cranking (look a the marks on an old starter), so 1/4" wouldn't matter much. Verify that the engine block is tight to the tranny case everywhere and there aren't any extra shims or plates where the starter mounts and the starter case mounts tight against the block and dust plate. Test the starter while you have it out and measure the extension with a ruler and compare to your engine.

I suggest measuring the voltage drop from the case of the starter (not the engine) to the big post on the starter, while cranking. My guess is <8 V which is why the solenoid is dropping out. All the starter knows is that dV. You likely have a bad ground to the transmission case or from the tranny to the engine. That is common with aluminum and bit me with a 69 Dart alternator and my Mercedes 300D speedometer cable started smoking while cranking.