which refrigerant?

[engine]

I'm planning an A/C upgrade on my Camaro (original A/C car). I installed new Delco evap and condenser the last time the engine was out. So now I have to get the compressor. I'm going to go with a Sanden/Seltec compressor, but haven't totally decided on which refrigerant to use.
When I first planned on installing the A/C, I figured I'd use R12 since I have a considerable stash of it. But now, I'm second guessing that for the sake of, "what if I run out"?
Problem is, my brand new un-used condenser is a fin/tube type, designed for R12. The condenser came with a tag that says, "For use with R12 or R134a Only. The use of any other refrigerant will void all warranties. If R134A is used, an auxiliary electric fan must be installed."
So this raised an eyebrow and I did some homework. Seems that R134A is best utilized with a parallel flow condenser with more surface area for heat extraction. My fin/tube unit isn't the best for it, and this will probably cause higher head pressures and less cooling effect.
I have already installed the Mark VIII fan and DC controller, so I'm sure I have enough cooling capacity to keep pressure down, but the condenser may still be inadequate.

So this brings me to ask, what would you do? I really don't want to spend another $200 on another condenser...