Steve,
I have had my 427 so for about 13 years. Several rebuilds ( I tracked mine a fair amount) but here is something else you might check. Check the housing for your dipstick and remote
oil filter. The only engine I ever had that didn't eventually leak was one I plugged off the dip stick. I ran that engine for over 4000 race miles and never a leak. I wish I had done that to this engine but I didn't and it does leak there. I prefer to pull the engine when replacing pan gaskets, bearings, or anything on the bottom because you can do a much better job working from an engine stand. Good luck.
Clois Harlan