You might get some information from this thread.
http://www.gasgasrider.org/forum/showthread.php?t=2228
There are some pictures posted there that might help
identify your motor. It may either be a Morini or maybe
an older Derbi. I have a picture of my 2002 Derbi SM 50cc
posted there.
I believe the 50cc GasGas SM motor to be the same as
the TXT70 Rookie motor and it is a Morini. Your 65cc may
also be the same bottom end......maybe not.
Good luck. Jeff