I thought about that, but knowing myself and how tedious that would turn out to be I thought I'd try to buy the right part instead. I'm starting to think I should buy some 1" header bolts and just go with it. I don't think 3/4" bolts will be long enough - the header has a 3/8 flange + the gasket, which leaves few threads to engage in the head. I can stick washers on the outside if 1" bolts turn out to be too long.
It seems odd that the heads won't take more than a 3/8" long stud though.