Dan. When I put mine back together I pondered the same things. I talked to a tech down in Florida who worked at an a/c shop. He said he converted his 69 to 134 and he wasn't happy with it. He said he didn't think the condensor had enough surface to cool the 134 right(?) I just put mine back with r-12. I sent my muffler and poa valves out to be tested and I had the muffler replated. The system works very well.