I have converted several R12 systems to R134a. I don't know where you get '96 as the year for R134a in American cars. This is a 1995 Ford Crown Victoria and I guarantee that it came from the factory with R134a.
I still have some of the compressor oil around here I keep the can so I know which one to get. It has the correct oil in it.
Changing all the seals sounds like a good idea. I think I even have a kit but I may have use a couple of them. I have this sealer stuff that is used on the O-rings. I didn't like it because it was sooo thick. Might use that too.