Lots of work - unfortunately yes..
It does sound as if your old compressor is stuck and probably bad.
If they are the same compressor the clutch should fit the new one however there is a special tool to remove the clutch. I was lucky and able to get my old one off by using a little heat and penetrating oil. Maybe a shop there would have the tool and take the old clutch off for you?
When using R-134 all the hoses and drier are supposed to be changed and the thermostat re-calibrated. The PAG oil that is compatible with R-134 apparently is corrosive to the old style hoses and seals and eats them away causing leaks. The new hose is called "barrier" hose and has a lining to prevent that.
The oil for the R-12 in the system now won't be compatible with R-134 freon and gets carried out of the compressor by the freon causing the compressor to lock up so the oil in the system needs to be changed if you are using R-134.
I think the only seals are in the compressor and sight glass on these cars. My other fittings were flare type with no seal.
That's the worst case - I have heard of many people who simply have their system flushed to clear out the old oil, replaced their compressor with an R-134 compatible one, add the R-134 freon and PAG oil and it works fine.
I ordered new hoses for my 1960 model from these folks.
I haven't finished mine yet - still a work in progress. I replaced the drier, condenser, hoses, and bought a new R-134 compressor. Didn't do anything with the thermostat or evaporator other than added an insulating material to the inside of the evaporator box when I had it apart cleaning everything.
Hope that helps,