i had kind of the same situation here picked up a motor with a rebuild tag on the motor needed nothing check your compressin and oil pressure if they are good should be a good motor
as for overheating look at thermistats,see if your rad is pluged up I know for a fact that these trucks need the factory fan shroud or they over heat
good luck and enjoy
My opinion? Keep your oil changed, run it 'til winter and then take it down - if you decide you need to. Flatheads are tough. If you have any compression it'll run.
Use some Marvel Mystery Oil in the gas and crankcase to loosen up the valves.
If your radiator is clean and the block is clean your heating problem should disappear when timing is correct.
I doubt you'll hurt the crank if you run as-is until winter. By then you'll know what you need to do and have some practical road experience with it.
My Flathead in my 51F1 sat for 17 years not running, it was last rebuilt in the 70's according to the PO. I mananged to get it running and the more I drove it the better it ran. That was three years ago and it's still running great and shows no signs on dying yet.