the oil required in a GM CCOT system with piston type compressor with R134a is PAG 150 oil (high viscosity), The clutch magnet wires are typical GM electric connector with a lifted ear and its near the pulley, to remove and install a clutch on a harrisson compressor you need a puller, its not like denso where the pulley can be removed by hand tools only.
That puller can be found at oldschool AC mechanics shops - as it was used in the Harrisson R4 compressors that were fit to mercedes benz W123 and W126 cars. - They used to call it "matka" compressor and the puller resembles the magneto puller of motorcycles.
the high side fitting on a GM is a bit fatter, so you may need a different coupler - its not that hard, a lot of hiace and mercedes MB100 vans had the same type of fat fitting. You can test it at a shop - just get the tech to attach the coupler and see if it locks in place.
That bolt you see would have a hole in the middle - its the high pressure blowout valve, it blows out the refrigerant if the liquid pressure gets out of control (e.g. a plugged orifice tube)
the low side is on the accumulator itself, the good thing about GM is that their accumulators are easily swappable around cars, e.g. you can fit a later model caprice/impala/caddy/olds accumulator in there.
Your condenser looks like its been in a warzone, clean it out externally and check for system leaks at 250 psi pressure - nitrogen works best. But being Pakistan, AC mechanics will use air, you will need to purge the unit with R134a before install and vacuum - unless you have a two stage vacuum pump.
This system is extremely simple, it works at fixed rating, there are a few electrical connections on it to prevent low pressure siezure, but otherwise its easy as chips
the manifold gauge set usage depends on the connectors on it and the scale on the gauges, R12, R22, and R410 are acme type threads, while R134a are quick disconnects, if you are buying acme type pipes then you would need to buy the quick couplers separately.
