Stephen, I have a 3.8 FHC that I converted to negative ground and fitted an alternator to it. There are two threads I started re. that endeavor. This first one is the summation of the project:
The initial thread is mentioned in the first paragraph of the above summation link. I settled on a Delco CS130 that has 85 amps. There is a reason to choose the CS130 over the earlier 10si and 12si versions in that GM improved both the mechanical and electrical noise. There are Denso options and, in the UK, Lucas is a good choice. I purposely did not choose the WOSP solution as I felt that they greatly increased their prices for a solution one can do far more affordably themselves.
Anyway, I hope you’ll find the links useful. -Scot