and no those little kits from autozone dont work
I used those kits on my 91 Mustang and my 87 Bronco. Both worked fine and my 91 Mustang still works fine 6 years later, the Bronco is long gone so I have no idea. It is not perfect and not as cold as it used to be but it works. If you have a leak that caused you too lose all of your original R-12, you will loose the R-134 as well so you still need to get that stuff fixed because the conversion kits do not perform magic.
There are "levels" of the conversion that you can do. Just buy the kit and go, you may be happy with the results (I was other than a small leak I have).
The other option is buy the kit, fix the leaks, flush it out with a cleaner, use a vacuum pump to clear out contaminants, old oil, and air, replace the o-rings, change the dryer, and replace with a more R134 efficient orifice or do anywhere in between those two levels. The extra money and effort will typically give you a better result. Depends on how much you want to spend.
My 88 Mustang was converted by someone else before I bought it and they put a new accumulator and hose on as well.