For three days I searched for some sort of rubber pan gasket for the 460 that came with my project boat. At least 7 different parts people told me that you can't get a rubber gasket for the 460. Finally one guy at Napa told me that there is such a deal but it only fits the new engines because the holes all have an anti crush sleeve and the four end holes aren't big enough to get the bolts through. He said he had tried to drill the holes bigger and tore the gasket to hell. At thirty five bucks that's a pretty expensive lesson.
I wanted to look at one of these things and they had one in stock. Even more interesting is that the thing is one piece, that is it incorporates the end gaskets and the pan rail gaskets into one moulded piece. I decided to buy it and try to figure out a good way to make the end holes larger.
Actually it was simple, take an exacto knife and carefully cut around the outside of the four end sleeves and you end up with the holes just a little larger than necessary. It should still seal fine and you just have to make sure not to overtighten the end bolts. I suspect that there are some similar gaskets out there that may incorporate a much larger crush sleeve that you might not want to remove completely. In that case you would drill a hole through a couple of pieces of plywood big enough to support the crush sleeve and still leave you room to work. Clamp the sleeve between the wood so that you can see through all the holes and carefully file away the sleeve with a rat tail file until your bolt will fit through. Do not try to drill the sleeve, there just isn't enough to hold onto and the bit will grab it and tear your gasket.