Rear main seal/Rod and Main bearings

[Dlowe]

An interesting day, I opened up the lower end to prepare to roll in rod and main bearings hoping to fix my low oil pressure issue, 62 lbs at start up and drops to close to zero when hot. Main bearing clearance's range from .004 to .006. Optimum is .002. Could be the culprit....Some of the journals have slight groves but decent overall. I'm not pulling it to clean up the crank. One issue is the mains only have a part number 3186677 with the AMC stamp and a manufacture date of 4/71....no clue what size? Anyone know? The rod bearings part # is 3186672, same AMC stamp and 500 stamped in as well manufacture date of 11/70. It surprises me that they are original bearings after 40 years. Rear main seal upper, I've found conflicting info, one says I can roll it in, the other says I must remove tranny? It's neoprene molded around an iron rod? Doesn't seem to want to let me push it out? Advise/experience would be appreciated. Thanks in advance.