81 300sd AC blown compressor would like to replace
 

I want to replace my compressor and most likely will need to do my evaporator and o rings at the same time... My compressor has a hole blown in the side the size of a quarter so i know it cant be rebuilt...

What is the best way to go... my Blower fan and internal temperature flaps work perfect.... I have been reading the forum on doing the o rings up inside the dash behind the blower.... What els do i need to keep in mind....

Is 134a the only option or what has anyone found to be the coldest blowing....