I was installing a new alternator in the 91 5.8 and found that the lower bolt that was in there is not the right one. It was way narrower, and looks to have been inserted just to keep the alternator lined up, but it doesn't really hold anything.
(the OEM threads are good, no damage)

Anyway - I want to find the correct bolt. I cant seem to find one. Anyone know where or what size the bolt is?

 

Have you checked Junk Yards ??

 

Nearest ones are pretty far - I will if it comes down to it.

 

Looks like I may have found it on fordparts.com Part #: 389483-S36, ordered

 

They cancelled the order- lol - at least I have the size now.