To be honest, you're better off sticking with the old original system. The price difference between R12 & R134 is way less than you will pay to upgrade your system to 2nd gen parts. To get an efficient system with the newer refrigerant you will need to change out the condensor at the very least. I went through this when I put the 5vzfe in my 84 and I'm very happy I stuck with the old parts and paid the extra $30 for R12. You only have 1 blower motor.
What exactly do you mean by ...'nothing coming out'? Is your blower motor working? The resistor for the blower on the first gens is delicate and will go out, leaving you with low and high only, or some other wierd combo of speeds. The vent ducting under the dash is notorious for leaking like a sieve on these trucks also so that barley any air comes out the vents. I siliconed the joints together on mine and had 3 times the air coming out the vents with that alone.
If the blower motor is working, pull it out, reach in there and clean out all the garbage that has accumulated over the years. You should find leaves, dust bunnies and a bunch of other crap stuck on the passenger side of the evap. While your at it, make sure your drain line isn't plugged up. Once you get all that lined out, I would get a new filter/dryer, fill it up with R12 and go enjoy some cold AC.
