Kit for switching from R12 to R134?

[ggtsvnv]

Hi,
I tried a search and didn't find what I was looking for. I have a question about switching the A/C in my 87 1/2 ton short bed to R134 from R12. I have read all kinds of different information such as "it's simple just change the oil" and recharge with R134 too "you have to replace all the "o" rings and seals to handle R134. What I was hopeing to find is a kit that has any or all seals o-rings or anthing else that needs replaced. So all I have to do is clean the old out, switch anything the needs replaced and recharge the system. Does anyone have a suggestions on such a kit or what needs to be done. I want to do it once and have it done for the next 10 years or so.
Thanks in advance