The Nostalgic Air kit is probably your best bet to have R-134A, all new parts and keep the two alternator 24V system. Anything else is going to need an alternator removed or an extra pulley added, rear battery and power strips moved and some other changes as well.
Don't forget that to get a factory air system from a SBS truck, it is going to be 20 plus years old, not be intended for R-134A use and probably need major components replaced. The money spent will probably come pretty close to what the Nostalgic kit will run. It is your truck so do what you want. Just pointing out a few things to consider.