No problem. O rings wont know the difference.
I would however see if there is an exspansion valve available for the R134.
Check to see if a 94 valve will fit, then use it.It is better calibrated for 134a . It will cool a little better, and more importantly keep the head pressure (high pressure side in the compressor) down so the compressor doesnt work so hard, and lives longer.
If you have O rings to replace the areas that you are dissasembling , use them. If not, as long as they are pliable, and are not deformed to the shape they are when installed under pressure, use them.When an o ring takes a set to a shape other than round, either circumferentially, or radialy they are NOT OK. Naturaly any O ring that is cut or split is a no brainer. Hope this helps.
Fact is stranger than Fiction