Are they the "clutch" head bolts, with a recess that looks kinda like a figure "8"? If so, there's a special wrench available that fits them. Once they're out, replace them with Allen bolts, or something similar that's easier to find a properly-fitting wrench. most professional-level parts stores will be able to supply you with clutch-head socket wrenches, or your friendly Snap-On dealer will have a listing on them, too. They're a little pricey, but necessary if you're working on an old Stovebolt!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!