Appleo, I have converted three vehicles, an 89 Probe, a 93 Taurus, and my old 83 F-150.
My pickup's a/c got very cold with the R134, though it took a bit longer to cool down than the R12. I would not do the conversion just for the heck of it, but if your system is in need of repairs anyway, that's the time to convert. Don't waste that rare R12 on a leaky system... waste of money and it trashes the environment.

 

My old 1988 has been a leaker from day one...and no dealer has found out why...I was gonna convert if possible...and cheap.......the old nag doenst have too much life left.

Or if anyone has some R12 I can use a few cans

 

I wouldn't do anything until the leak is found. Finding a leak in an older F150 with the evap coil in the engine compartment is easy, that is if you got a leak detector that works PROPERLY.