A/C cluth, compressor or 134 conversion???

[BBrendal]

Ok heres the deal. My Blazer R12 system holds a charge and blows cold but the clutch on the compressor is tempremental. It has alot of resistance and is hard to turn by hand or will even squeal the belt. I changed and tighted the belt and its a little better but not right. If I turn the A/C on while cruising it squeals. If I turn it on at idle a chirp and its fine but go over 40 it squeals. I want to change the clutch because I dont want to break ofen the A/C system but I never done this before. Is it hard to do? Ive worked with 134 systems but just swaped the compressor on it. Not to much experience other then a charge or o ring change on r12 systems. The other option is to change the compressor but what else is involved in that? If I do that should I just convert to 134? How hard is that? Im leaning toward swaping the clutch and having a nice day. I really dont want to crack the system because there is no reason to. I still have about 14lbs of R12 so I could add if it need a shot. Any advice, direction or sugestions are appreciated.