GammaFlat: OK, I see now. Your point is the impulse step function of force from the impact driver would outperform a more gradually applied force. Indeed, on those studs I did by hand, I often got better results by "running at" the wrench or vice grip, a sudden tug/push vs. a slow steady one. On one of them, I only got it loose by whacking the end of the vice grip with the sledgehammer. Same principle!
MCRider: It's a bit late. Unfortunately, on 2 of the remaining three, neither a stud remover not an impact driver will help. For the one, I've already bent it into an L shape (see above pic). For the second, just straightforward torquing has started to bend it in an alarming way about 1.5" up from the crankcase, so I'm planning on vice gripping that one at or below that point instead. I might give a driver/remover a go on the 3rd one, though.
I've decided that tomorrow I'll get a smaller vice grip pliers, one where the curvature of the jaw will more closely match the small stud (and not tend to just rotate),
and a new stud remover. It'll give me a chance to get another propane cylinder to heat the block as well, and have the Sunday morning donuts and coffee, too
