So the sticker for R12 says 6 oz of oil does that still apply with 134A since you use only 80% of refrigerant compared to R12?
At this point I only plan on flushing the evaporator core and the hoses and hardline, the compressor, dryer and condenser will be all new.
I don't see why not. Whatever the refrigerant can carry is what it's going to carry, any excess will just be left behind in whatever pool it happens to be in. The amount of refrigerant comparison doesn't really have a lot to do with the amount of oil.
I honestly don't see much of a problem with having a bit more oil in the system, so if you happen to toss 7 oz. in, so what? You just don't want to go below minimum for the compressor's sake. There's nothing else in the system that needs the oil. Some of the oil will get sucked up into the new dessicant anyway.
You're going to probably get different answers to the same question. I put 6 oz. of ester in my 84 when it got converted over to 134a, and had no issues with it until I decided to go back with R12 after the reman compressor sprang a leak.
As far as the oil in the compressor,
Bonnewagon , the 85 and 87 Olds Cutlass CSM states that if you pour out LESS than 3 oz. of oil into a measured container, then you put back 3 oz. If you pour out MORE than 3 oz., then you put back in what you measured. But minimum would be 3 oz.
Oh, and make sure your new accumulator has 134a dessicant in it. The original R12 dessicant won't work too well. Most new aftermarkets do, but just make sure it does.
Now, with that said, there's this.....(for a 3rd gen Firebird, but it used 8 oz. of oil in the system anyway)