Siezed Crank pulley bolt

Trying to do the lower timing guiderails on my 1985 500SEC. The Crank pulley bolt is REALLY seized on tight. Got the 27mm 6-point deep socket and 4-foot breaker bar. Cannot budge without turning engine backwards (bad thing) Even tried the starter with the breaker bar wedged on the floor but the whole engine just shudders and acts like it is about to jump off its mounts. What is next? I don't have air for a pneumatic impact wrench and even with the radiator removed I think I will need a right angle electric impact wrench!? Does something lik this exist? Any other ideas out there about removing a stuck crank bolt? Thanks, Brant