I know there will be some obvious opinions on this, but having done my share, Ill just say what I know works very very well. In fact I co wrote and did the research on a bulletin for the AERA ( American Engine rebuilders Association) on this. The Solution I received from member Pontiac Gregg , a bunch of years ago, actually really works well. The "Indian adventures" rear main and one exactly like it are fairly "thin" and in 400 applications, on older blocks fit in the big valley of the rope sortta well. On the 455 its a bit different story ( especially the 75-76 blocks)
What he does, and I did , and have done, and now my 1970 4 bolt has it, is get a Caddilac 500 cu in Rear main seal. ( same size crank) Its bit wider base , and lip is a bit more firm all the way around the crank. Its not a seal made for a smaller crank( 400/350) that was enlarged for that engine as the other Pontiac ones are.
Take the crank up after cleaning the rope galley with alcohol, or wax and grease remover, lacquer thinner, and dry it, put a bunch of black RTv in the rope Valley. then install half the seal. sit crank in it carefully, ( old bearing in place)then lift up and wipe excess. Do same for cap, ensuring its filled at bottom with sealer. Put on cap,( bearing in place and tighten, then remove, lift crank some and support, and let both parts dry apart over night. Use a razor to clean mating surfaces next day and install with a tiny drop of oil on each lip. The caddy seal is better suited for the "big valley" and the RTV makes sure nothing sneaks around it. Have done a 70-72 and 73 455 now this way and there are dry oil pans/flex plates etc!
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