Congrats on your first Enfield. They are unique machines and well worth the effort to enjoy.
Judging from the numbers you supplied, I would suggest your Enfield twin is a 750cc Mk1 Interceptor produced approximately 1964-ish.
The best thing for you to do is reach out to the REOC dating officer (Mr.Graham Scarth ) and forward not only your motor number and frame number, but also the gearbox number. He has access to the original factory record books and should be able to give you specific info for your machine.
You will find the gearbox number stamped on top of the gearbox and should be a combination of letters and numbers.Example: AGZ1234
If original to the machine that SAME number will be stamped on the right front of the crankcase.
You can also find more info on the Yahoo Interceptor Group and also here- http://www.ozemate.com/interceptor/
Parts and more help can be had by visiting hitchcocksmotorcycles.com
Hope this helps