GM went to metric bolts on new body designs starting with the downsized 1977 cars, yes. But the engines continued to use SAE, again until they were redesigned.
The van body was largely unchanged from 1971-1996 and retains standard fasteners for body bolts. Some metric stuff begins to appear in the dash when they change to the last style about 1983, so they're mostly smaller fasteners.
So if you have an SAE toolkit and throw in a set of 5-14mm sockets you should be able to handle almost anything on there. There are some Torx screws also, 10, 15, 20 will handle most of those.
Conversions seem to use whatever the conversion outfitter had handy at the time.
Last edited by pontiac59; July 29th 2021 1:37 am.