I think I better re-do my oil pan...

[Destroyer]

I haven't worked on an I/O in a loooooong time, but if I remember correctly there should not be any pressure in the oil pan. That's what the engine breather (PCV) is for. It scavanges the fumes in the pan and burns them off through the carb. So you shouldn't have to worry about any pressure forcing oil out the pan lip.

Having said that, one sweet little trick you can use is to make yourself a few pressure extenders. Basically all it is is a short length of metal (about two to four inches in length and about 1/2 to 3/4 of an inch wide. 1/4 inch thick should do nicely.) In a vise bend the tips of the metal bar about a 1/4 inch from the ends. (Just a little, 10 to 20 degrees should be fine) Drill a hole in the center wide enough for your pan bolt to go through. (Use a new pan bolt slightly longer than the original to make up for the extra thickness of the bar). Put the bolt through the bar with the bent tips facing the pan's lip, then use them on either side of the broken bolts. The extra thickness and the slight bend will create extra pressure on the pan lip closer to the broken bolts and will help make a good seal. GM used to do a similar fix like that on the valve covers on the old Chevy 283 engines. If you have a good junk yard nearby and they have "old" cars you even might be able to find a few and save yourself some fabrication time.