I also just noticed the acumulator has an R12 sticker with it, not on the can. Well, I never get in a hurry so it can wait.
I believe the accumulator (receiver / dryer) for your year's "R12" system has different thread pitch on the fittings than those on a later "R134a" accumulator (e.g., which might be used on a 1995 truck). At least, this is a problem I had on a 1995 S10 I was working on recently... an earlier "R12" accumulator looked like it would fit, but the threads would not play well together with those on the OE R134a evaporator.
Ditto with switches, which is why
@L31MaxExpress mentioned the "find" of a cycling switch appropriate for R134a that had the proper fitting for an "R12 vintage" accumulator.
I believe you can use an "R12" accumulator with R134a/PAG in the system, so that cause is not lost AFAIK.
I'm treading into new territory here, but... My belief is, if you bought new parts for
your particular vehicle year, you'll be OK. If you tried to mix and match, e.g., a later R134a-vintage receiver / dryer and perhaps a hose assembly (e.g., from a 1995 truck, which
seems intuitive) , with some existing R12-vintage parts already on your truck (e.g., evaporator), the fittings may not join. Similarly, if you were to replace ALL the R12-vintage parts with those from a R134a-vintage year (1995), I expect they will fit and work fine. I have not proven this.
If you haven't checked your fittings to make sure everything's going to mate, you might do that ASAP.
(finally, some misc thoughts on R12 follow, feel free to ignore)
For the record, there are replacement refrigerants for stationary applications which originally used R12, e.g., grocery store stand-alone chillers, U-Line ice makers or SubZero refrigerators made prior to ~1994 to name only a few. R406a is one such replacement, composed of a mixture of gases (three, I think). While there are reasons for not using R406a as an R12 replacement in older autos (e.g., leakage, a common problem in such systems, causes fractioning of component gases from the refrigerant and so changes its properties), there are people who do use R406a in their vehicles as an R12 replacement. Google it. R406a traces its roots to a professor at Purdue who, around 1990, dabbled in refrigerants, outside of his field of specialty (PhD EE). This is, at least, as I remember it. A friend of mine was one of his students.