as my good friend in jamestown ny says [he has been in the vehicle repair business over 50yrs] there are no ny titles from 1973 back. all you get is a transferable registration.
is it possible the ny buyer/owner never registered the vehicle, and it is still titled in pa ? or he still has the pa title ? [or copy ?]
it's been a while since i did an out of pa transfer, so i would suggest you go to a notary public or a place near you that does transfers on a daily basis, and ask them the proper procedures needed to do an out of state transfer.
there are papers that will have to be filled out, as well as having the serial number verified.
it can be a pain or not, depending upon if you get a good person to help, or someone who couldn't care less about an old car.
you could also look up some of this stuff [i think] on penndot's main web site.
i don't know if this has been any help or not, but i hope you make out good, however it turns out.