Hi
As long as the system is vacuum purged & there are not issues already
existing, it should be fine using existing 3.6 compressor.
Not sure about condensor, but I am not aware of any functional issues on the parts.
Hope not.
We have serviced & converted one early 3.6 & its running around on R134a
just fine...at the moment

, but we changed all the gaskets & "O" rings.
The issue lies mainly with old "O" rings & gaskets that were potentially susceptable to
being broken down by R134A.
New "O" rings & gaskets should be fitted on an old system about to be converted as part of the service.
R12 is a much more efficient refridgerant medium than R134a but its also much
more of an atmospheric pollutant, hence its demise.
Cheers
Farrell