Skidmarks,
Yep, the oil pan has to go. As 3B suggested you may need to loosen the remaining caps. The 58 rear mains were not machined for a neoprene seal, but if 3B has one, I wish I had known about it a bit earlier.
I just finished the same task, and put a rope seal back in. Loosened all caps to get enough clearance to pull the seal through, and you can do this without removing the oil pump screen.
Good luck,
