This is not low buck advice but you might stick it under "if I ever win the lottory". Vintage air in San Antonio is the priciest but they do most of the product developement with an actual car on site and have super tech support. Many others wait for Vintage to bring something new out and then make a knock-off of it. The easiest mounting and nearly invisible unit is from Air-Tique in Cleburne, Texas but, it uses all vacuum pots to actuate the different functions which is not good on long cammed rods. Finally, Old Air Products in Ft Worth has some econo offerings that work OK. Selection is good but tech support not up to Vintage standard. Remember that with R134A freon that condenser size is very omportant, it just doesn't work great with a small condenser. Not such a problem with a pickup but a killer for a big old 4dr sedan.

Evan