I had the same thing with an Optima yellow top went to tighten the positive terminal clamp and the post came out of the battery I think they went bad when they started making them in Mexico. Had a US made red top lasted over 10 years and wasn't even well looked after.
That blue looks like a rust proof coating if it was blue from heat definitely wouldn't come off easy. There's no blue where the bearing sits which would have been ground zero for the heat. If the bearing is a little loose on there you can stake it a few times with a centre punch to reduce...
If you removed the transmission there could be a bolt or tool accident left in the bell housing area that jammed against the torque converter then when you rotated it the other way it move out the way, crazier things have happened.
Change the oil and filter after the first start and cam bed in to get all the grease and other impurities out. Use break in oil or a basic mineral for a while before using any type of synthetic oil.
It has a H so would it be a 340 car? If so why BH not BS? Were the VIN tags screwed into the dash pad when new or was the dash pad replaced at some point?
I would just keep it in dry storage and leave it alone, why waste time/money if your not going to use it. A freshly machined engine needs to be used or the internals will rust also why modify and stress you matching number block the last thing you want is a failure of that irreplaceable engine.
Try R/T specialities they have a lot of Mopar specific fasteners and next time screw the fastener back into the part throwing them in a bucket or drawer with others is a rookie move.
The car I need it for is a real V code so I would prefer original but I can't even find a reproduction set. I have been in touch with A & A Transmissions and a few other vendors and no luck.