I just think that the crankcase is $20, maybe $25 with shipping. You're going to spend how much on materials? You've got minimal surface area to work with. That patch you're looking at depends on surface area to work--they're designed for auto mufflers and such, where surface area just isn't an issue.

It's not hard to disassemble an engine. There things you have to be mindful of, but it's not tough. Seeing as you don't appear to have the firewall put on yet, the plane can't be ready to go.