hi   still in florida but will getting back to conn,end of year my a/c on my 1979, I need to check pressures , I need to know where high port is and low side port,it always worked and still has r-12   shop manual  said no need to hook up high gauge,to dig  I need to know pressures,thank  david

Chances are its the port on the manifold on the back side of the compressor....unless there is 2 ports there... however, if you follow the line coming from the firewall to the compressor then thats the low side....the line going from the compressor to the condensor(the smaller radiator infront of the radiator) that would be the High pressure side.....   normally you do not need to check the high side if things are working properly, the low side is used for charging the system with refrigerant.  Pressure reading should be in the 30-35 psi range....and should not drop below 26 psi(or so) when the engine rpm's on the higher side(4000-ish rpm),   if the low pressure switch works, it will turn off the clutch to the compressor untill the pressure returns to something higher.  

I know R12 is expensive (paid $200 for a 20 lb tank in 90s right before it was outlawed), but think twice before changing to R134a as while it will work, it won't cool as well and the two oils aren't compatible.  Also the seals aren't compatible.  There are other substitutes and some contain propane or butane and that certainly isn't very safe.