To answer both "Keoke" and "CaptDon01" in one reply....
IMPACT WRENCH? What on earth would I do with one of THOSE? /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
As for keeping the crankshaft from turning, I can only speak from Spitfire experience. What I've always done is to put my socket on my 3/4" breaker bar, put the whole thing on the pulley nut...and then hit the starter button. Sure, it sounds painful and damaging, but you can always put a wood block where the bar will otherwise hit the chassis. I've yet to hurt anything, and I've yet to fail to break the nut loose with this admittedly barbaric method!