Ryan,
The studs and bolts on my '85 exhaust are all M8.  When I fixed mine I used a combination of studs and round top bolts with allen key heads.  The allen key tops were much easier to work with than the hex heads that were there.
Have fun.
George
'85 Westfalia

Subject: Exhaust Stud size

I seem to have lost on of the studs out of one of my heads (85 1.9L).  I
know I have extras of these at my parents place, but that doesn't do we a
ton of good.  Since there an hour away and it would involve digging through
boxes of parts to find one.  Does anybody know the thread size, so I can
pick one up