When i rebuilt the 283 in my 57, i had it bored .060 over.
When i put it together i got the old motor manual out and read all i could find on rope rear main. Was maticulous on assembly. Oil leak at rear main. Luckily on the 57, all you had to do was drop the drag link and pan was clear. Got a new rope seal and repeat, oil leak. Luckily got another new rope called my old mechanic/machinist, and he came down and did it his way. Oil leak😡 Dad found a guys ad in Hemmings motor news and he made a 2 piece rubber main seal and garanteed it to not leak. I sent him my $8.00 and installed it..... no leak at all😁 In the time i had that car, not a drip of oil or anything else at all.
When i restored my brothers 67 RS conv for his wedding present, i replaced the heads. I headed to California for wedding. Got into Arizona as the sun was coming up and seen light smoke and could smell burning oil. Jumped up on off ramp to check, oil all over the back of engine dripping on exhaust. I had tools etc in trunk, found a rest stop. Thought valve cover leak, nope. It was the rubber rear seal on the back of the intake. Tore all down to clean up and reseal. Couple young guys stopped to look at the car and walked up looked and said we get to the next town we'll call a tow truck for ya. I told them no thanks, just an oil leak i'll be done before long. It does look bad when you have air cleaner/valve covers/ distributor/ intake all laying on towels beside the car😁 i thanked them and in an hour and a half i passed them on I-40 waving big. I thru away the rubber and just sealed it with silicon atv. Found a car wash and got all the under carage clean. End of oil leak.