The low and high side pressure should be within 30 psi of each other when things are working properly. High pressure on the low side could be a defective check valve or when there is higher than normal pressure on the low side or it reads higher than the high side it indicates a compressor problem. Sounds like your compressor is leaking severely and already damaged. I would not attempt adding any more R134a refrigerant because its way too high as it is.
If you want to DIY the AC I'd suggest getting a good service manual.
Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials