If you want it pretty do a search for "high mount alternator bracket". If you want a sure enough strong one cut a piece of 3x3x1/4 angle about 8" long and drill a pair of holes that line up with the front and front center exhaust manifold bolt holes. Use a 7/16 fine threaded nut between the angle and the manifold as a manifold clearance spacer and tack nuts to keep in place. Weld two alternator mount ears on top of the angle (or weld/bolt a factory bracket to the angle). Our 302 Ford air compressor and our sbc V8 fork lift (no kidding) are both done this way. The 302 engine runs on 4 cylinders and pumps air on the other 4 so it shakes enough to give any bracket on it a good test.

Evan