what should my a/c pressures be for r-12

[bautino95]

I have an all stock 1971 402. The a/c blows cool but not cold. I have a few cans of r-12 laying around still .I did a search but can find what the high and low side pressure should be for a stock r-12 system. I have an old A/C book laying around and for GM with SVT it says low should be 28.5-31.5 and the high should be 210-260. does this sound right? Thanks