Due to R134 and R12 being different gasses you need to change "some" parts which are suitable for R134a
all hoses
receiver drier and prussure switch
thermal expansion valve, with one adaptor to fit the valve to the evaporator. New tartape in order to repack the new expansion valve.
Flush condensor (getting rid of R12 Oil)
Compressor, I fitted an SD514
add 2 service ports to the hoses
As the connections on the new sanden compressor where radialy mounted you need 2 "short" 90 deg hoseconnectors
Fill the system with R134a and maybe some additional oil (usually there is an amount of oil in the new compressor)
It cools the cabin more than OK, but I have no camparison against a working R12 system. (In my opinion the glass sunroof also does marvels for putting heat into the cabin)
Big job but doable, hardest part is removing / routing the hoses through the sill cover (just remove it and refit) and under the fueltank.