I kept the original system....POA valve / with A6 compressor, I did convert to 134freon. Did have the POA valve checked & tweaked for 134 freon.
I reused the A6compressor, all hoses, condenser, & evaporator.
I replaced the dryer, expansion valve, and all o-rings.
Also bought the 134 low & high side conversion fittings from NAPA (nice HD brass units.)
Classic auto air was a great help (parts and advice / thanks Curtis!!!).
The Auto Air Forum is a wealth of info->http://www.autoacforum.com/
I took my time.....read the forums and am very pleased with the result (mine cools to 38 degrees at the dash vents), plus I still have the original system.
Here is link to my conversion....info, (pics too)....