Is it ok to set top dead center with heads off? How would I know if it is set properly?

 

not sure what you are asking. If you are wanting to make sure TDC of the engine matches the 0 deg mark on the timing mark: You install a piston stop (to stop the piston from coming all the way up). Turn the emgine slowly until it touches the stop. Then mark where the timing mark is in the damper. Then turn the engine the other way until it just toughes the piston. Mark the damper again.
If the damper is correct (not slipped), both of your marks wii be equal distances on each side of the factory mark.