My '93 came with R12. There have been a couple of magazine articles recently that converted to R134a by replacing the entire system. In this way the usual 'doesn't cool as well' didn't apply because everything was apparently sized correctly.
There are replacements for R-12 these days, FR-12, I think. I had a '92 and it used R-12. I've got a whole 30 lb. container of it in my garage, worried that it'd be hard to get.
Oh, you can use propane too. (good idea, Batman!)
Also, the '92's are the last year to have forged pistons, FWIW.
I had an opportunity to talk to a Ford Parts guy a few days ago, with a little looking, he came back with the conclusion that early '93's were R12 and later or latest '93's were R134. He said he shows R134 parts for '93's. He didn't seem too confident in the information though.