[mr48chev]

I'd go along with what's different than before and look there first.

With the two wire alternator, how is the exciter wire hooked Up? Through a keyed on circuit or direct? Direct might cause a draw when the switch is off but not cause the engine to keep running.

Also check across the top of the battery from one post or another to see if you have current flowing across dirt or moisture on top of the battery. I've seen some serious draws with dirty battery tops in the past including one that killed the battery in three or four hours on a student's truck when I was teaching.