500 for a M112? that is cheap! I picked up my M90 off a supercoupe for $66, along with all the plumbing and intercooler.
I talked to Ron Caster (the guy who makes the kit for putting an M90 on a 4.0 SOHC) and he says he is currently developing a kit for the M112. He didnt say when itd be done but it might be wort hwaiting for.
And also, if you buy a water/methanol injection kit, you can run a few more lbs of boost