Your link says:

GM R4: Drain and measure oil. Replace with the same amount of new oil + 1 oz. (3 oz. maximum). Add 1 oz. for drier.

From Yak's DIY Compressorworks R4 writeup: "The FSM section 83-520 has specific quantities to add depending on what you’re doing and how much oil you’ve removed. The compressor re-install section, 83-522, says a total capacity of 170 cc, or 5.75 ounces."

So I gather the recommended range is 4- 5.75 oz. which puts me at 2 1/4- 4 oz. (shop added 8 oz.) too much oil less what spilled when he put the compressor in. When I attach the manifold to the high pressure valve, oil does squirt out. I may have to squirt some oil out to get the pressure down and recharge one 6 oz. can. You can search forever and not find any definitive answer to the oil capacity for the R4 compressor, thanks.