I have considered the same approach for an alternator, but as you already know a proper stand alone bracket is the way to go, if you can make it work.
Problem with that could be finding or having made or modified a crank pulley with two groves. That was my problem when I cam up with the piggy back idea, I think there are crank pulley options now though. A factory one being a 235 or 261 that had a factory air compressor is supposed to have a double grove crank pulley, but this is a somewhat rare option and only on the bigger trucks if that.
Check out this guy, he may be able to help:
http://members.aol.com/damperdoc/The pump I used came from an IH pickup, but is the same as used on GM vehicles of all sorts for many years, later ones had metric fittings and bolts (approx 19980). It is a Saginaw P series pump, often called a "caned ham" pump because of the reservoir shape. I also had an aftermarket rebuilt/upgraded one from AGR, but I think I'll use regular auto parts store rebuilds in the future.
Grigg
