Best is a new parallel-flow condenser, since they typically give ~30% more cooling. You can find posts here w/ photos and somebody sells a hose kit that makes conversion simple (ebay?). These are almost mandatory w/ R-134A and certainly help if R-12. Next time the 84 is home, I'll compare its condenser with my 85.

I will be fixing the AC in both 300D's. I wouldn't dream of using R-134A. It is inefficient, corrosive (PAG oil absorbs water, plus R-134A may degrade), and soon to be outlawed (new is maybe R-1234yc). Indeed, I just replaced the compressor in my 2002 Chrysler, so flushed everything (new filter & exp. valves), and refilled w/ mineral oil and Duracool (HC mixture). Works even better than R-12 and have used for years in my 60's cars. But read up because many fear it and shops conspire against it.