Re: Crank mount raw water pump conversion question
Any disadvantages, and I'd have to say NO, there are only "advantages".
He'll need the space in front of the engine to accommodate the pump depth.
I don't recall if the 5.8 FL in 1995 used the serpentine belt or not. If so, you may need to fabricate alignment dowels for the pump flange.
IMO,ypu'll end up with a better pump system with no side load from belt tension, and easier impeller access, etc.
He can find a Johnson F5B-9 on sale occasionally for around $150, complete with new impeller.