Chad and Thief, You are both going to probably skewer me but I did my own conversion on my 87 pickup from r12 to 134a around 3 years ago. With the help of my neighbor who used to do AC work years ago. He had the vacume pump and gauges to make it happen.

I had a very slow leak so I had no r12 to get rid of. I used a Castrol brand conversion kit that included the new fittings, a can of stopleak/conversion oil, and a can of 134a.

We changed the fittings pulled vacume for awhile, added the can of stopleak/conversion oil, charged the system and it is as cold as I remember the r12 system ever being.

Total cost was $50 IIRC. At the time folks on the lists told me I had to replace my receiver/dryer, o-rings, compressor, etc. I did not replace jack and it works like a champ 3 years later. The leak is even gone, I have not added any 134a in three years. In the past my r12 was gone within 6 months.

I am sure what I did is not "technically" the "right way" to do it. But there was no way in hell I was going to pour hundreds of $$$ into a truck worth maybe $1k. If it failed I was just going to remove the stock system and install a york for OBA.


Disclaimer:
This is just my personal experience and I in no way endorse what I did. I am not certified in anything automotive. Just shadetree.