Did you contact Colt?  They have a full-time historian and for a fee they will do a historical research letter for you.

I am too kind of interested in this..
Looking to get a FA M16,and seeing a model 614 as a good deal at the moment..

These were Air Force guns i understand? And what was the deal WO the forward assist?

Thanks for any info..

Brenden

MP,
    As of the last time I checked, Colt will not research their FA rifles for individuals.

Doc,
   As long as "CONSENT TO DISCLOSURE" (box #9) on the F4 was authorized, you should be able to get the info from BATFE NFA Branch yourself. If Authorization was not given, you can get the info once the NFA transfers to you. Do A FOIA request on your rifle once the transfer goes thru for a hard copy of the date it left Colt.
    All Colt barrels I have seen are marked somewhere. Are you sure the bolt was marked "MPC" and not just "MP" in large font? Post some pics of the bolt & carrier assembly when you take possession. Also, tell us what type spring guide or buffer you have in your rifle, an Edgewater type or rifle buffer with dark plastic tip. Many of us are interested in info on the older Colt FA rifles.
                                                 
                                                 HTH,
                                                 Carey

Edit: Doc, Congrats on buying a nice piece of Colt AR15/M16 firearms history!