72 GTS: Since your engine is out of the car, it would be a lot easier to replace the rear main seal now rather than have the engine in the car and realize the rear main seal leaks; otherwise you'll have to pull the engine to replace the seal because the cross member will not permit the oil pan removal to access the seal. (a number of Pantera Forum articles outline a removable cross member for access to the bottom of the engine.)
You do not have to remove the crankshaft to replace the rear main seal; however, loosening the the main bearing cap bolts and lowering the crankshaft 1/32 inch is the procedure outlined in the Pantera service manual to access removal and cleaning the seal grove.
