I was able to borrow a puller from O'reilly a few years ago under their loaner tool program. I would see if you can do the same at one of your local stores. They only had one, and it fit.
I suspect it is metric because the R4 was used on the later model trucks when everything started going metric. My friend's '87 used the same compressor, so yours probably does too.
I have the puller from my '86 at home. I ended up buying one because I kept borrowing it from the parts store so often. I haven't needed it since then, of course...
Slonaker