Hello Greg,
My xverters are not GPS locked, but I do have the TCXO in my 817. ?My guess is if you lock your PLL on your xverter the 817 will be close enough for what you need to do. ?I would ?think for even JT-65 it would be close enough. ?I just picked up a Kuhne PLL for my 76 GHz xverter, and I plan on using a 10 MHz OCXO on that.
Good luck and 73,
Mark ?WB8TGY?