The USGI connector lock is about 1/8" longer and a few thou larger in diameter. This few thou will require some turning on a lathe (if have access to one) or chucked up in a high speed drill (3000 rpm or greater is lovely) and then take a hard file back and forth to turn down the USGI connector lock pin. Been there, done that! It's freakin' hard metal.
Then once it's installed into your Norc receiver, it still sticks out about 1/8" (hence the name, "Popsicle stick fix" ) for the M14 connector lock (which is a FA part that will be useless for any FA conversion).
Hope this helps.
I can direct you a source for this connector lock , USGI NOS.... send me a message!
Cheers,
Barney