Supplementary Post

The top view of the design including the new engine, alternator and batteries will be something like the figure below:

I probably will have to move the front crossmember forward slightly - easy as it is bolted in.  Also, I will probably have to adjust the center cross member - harder as it is welded in - or move the alternator to the rear more if I use smaller batteries.

Currently I am searching for a (hopefully) standard part like the following:

A blade adapter for a mower that slips over the shaft which holds the blade and provides a pulley for the alternator.  Normally these types drive a transmission for self propelled mowers, and the pulleys are about 2.5 inches in diameter.  If the engine turns at 3150 RPM, the Alternator should turn at about 4500 RPM for peak efficiency, I'll need about a 3.75 inch diameter.  I'll probably have to make or modify one.  Some of these are cast pot metal, but some are steel.  I could cut the pulley off and weld on the correct size worst case, but for now the search continues...