Check out www.powerbastards.com, I just picked up the Fitzall 220 unit that puts out 110 amps at idle and a full output of 220A. It is a very nice new unit at a good price. It may not be exactly a drop in but its pretty close, very similar to the Denso unit. I needed to put a bushing in the mounting hole to go from a 1/2 bolt to a 3/8 mounting bolt (got it from McMaster and I have a spare if you need one).

The power lug ends up about 3/4 inch from the head, a but close, but no closer than some factory GM stuff I have seen.