What exactly is your application?
Interestingly, RockAuto lists the applications as being (only) 1990 C/K pickups 1500/2500/3500 (I won't assume, necessarily, all models).
Here's the parts explosion from RockAuto for that kit, you might investigate each part individually for its applicability.
The claim that the compressor is "prefilled w/ OE specified oil" leaves me with a few questions.
You may wish to take a look here; I did, but didn't see any indication of R134a applicability.
I realize that it's impractical for any mfgr to sell an R12-specific part, given the fate of R12. Then again, I know guys that still have a 30# can of R12 on hand (me) and also have access to other R12 "replacement" refrigerants (for whatever you happen to think of
them; I'm not a fan of refrigerant blends when used in an application that's likely to develop leaks, e.g., automotive).
At one time I myself looked into that scroll compressor but for some reason decided against it. I seem to remember that the scroll compressors had some characteristic that I felt undesirable (poor low-speed pumping capability?); maybe someone here can comment.
Instead I set my sights using a Sanden replacement instead of the R4.
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