I'm working on a post about 5 series model bloat and came upon this one-off. (If anyone knows the cargo/trunk capacity of the E28, let me know; that's the last piece of the puzzle for me.)
Matts Kinby started off with an E28 M535i (which in turn is a regular 535i but with a different suspension, wheels, and body panels). Then, he added an E34 M5 engine, lighter brakes, BBS rims, race suspension, racing tires, and enough customized body work to make a dekotora truck owner envious.
More info here.