Mine is five digits earlier then yours. I did a FOIA request and I will double check but I believe it was registered in 1971 and the moderator registered in 1974. I heard Colt made them with the leftovers after the switch to the EX177E2. Certainly not a lot of them around.
Edit to add:
I just checked mine was form 2 registered with a group of 20 Commandos in July 1972 and the moderator in 1975. I was off a year...
Buddy has pictures of this one in his picture collection.