Fitting new lower mounting bolt
The original generator bolt is not long enough; you will need a 7" x 3/8" bolt. I chopped off the head so  that I could clamp the left side of the generator bracket as shown - this to avoid the bracket being bent by tightening the alternator. In retrospect I think leaving the head on the bolt would fine, since the inner nut on the right side is really doing the work. The generator bracket's front hole is larger than 3/8" so I filled it in a bit with the mig and then reamed it up to 3/8"; otherwise the bolt could flop around. The engine mounting plate's hole is also >3/8", but since the generator bracket's front hole is now locating the bolt I didn't bother about it. There is a thin flat washer between the engine mounting plate and the alternator. Also, the top surface of both the generator  bracket and the front engine plate need to be ground down a bit to make room for the body of the alternator, so that it can swing in close to the block for installing the belt.