Have a 68 nearing completetion and wondering what your thoughts are about impacting resale value.

None,

Just let them know. Am assuming still original equipment (or original looking). If they want to go back to R12 is very easy. Put the 134a in, then remove the valves. If you go to sell it, not only tell them, but put the 134a Valves in the glove box in a bag. A thread was just asked on this a few days ago. I could not find it, maybe you can.

If you want to drive it to Albany,NY I`ll put some r12 in it for you.