R4 compressors themselves are generally identical besides differences in coil clocking and possible manifold variances. Some coils are 9 o’clock and some are 12. That’s not the end of the world, though, to have to work around. You might have to lengthen the pigtail in some, but not all, cases. The original Delphi/Harrison compressors had some variances in suction/discharge port diameter, and some hoses had pilots while others didn’t. The new ones have a uniform manifold design and use different spacer seal combos to compensate for hose block differences.
@CorvairGeek can likely elaborate on this better. Correct hose blocks are part of making new hoses so that’s not a dealbreaker either. I believe the A6s utilize either a 2 or 10 o’clock coil clocking, but the suction/discharge sizes, not to mention the manifolds themselves are the same. I’ll admit to not knowing these like the R4s and V5s, though.
The R4 pancake is an inferior design to really anything out there. That’s not to say that an individual compressor can’t go for many miles and work quietly, it does happen, but their design makes them more prone to not do either. The new ones have been built only by Comp Works/Four Seasons for like 25 years so there’s that monopoly. The A6 is solid, effective, just outdated compared with how designs improved over time like with Sandens or the Delphi/Harrison V5 and V7. They’re more expensive to deal with and very heavy to do what they do, but I would be open to resealing one. Even an R4 that didn’t have a lot of miles might be a candidate for a reseal, but if it had more than 80K, I’d junk it if it puked around the shell. I think puking around the shaft seal is more of an A6 attribute, but they’ve since come out with a better than OEM shaft seal for those.
