First of all, if the temperature where you are doesn't get hotter than the nineties, you MIGHT get by with R134. I still feel that if you will get the system leak free and stay with R12 you will be better off.
In the event that you decide to change to R134, use the green o-rings. These are for R134.
Also, you mentioned the auxilliary fan. It not working won't necessarily blow the compressor, but it is really hard on the compressor. When the fan comes on, it brings down the high side pressure. The R134 system is kind of difficult to get charged exactly right, and the high side pressure can "run away" which loads and possibly blows the compressor.
Best of luck,