I have a Colt "N" marked buttstock that's been reamed to fit a NON-Colt 5 position buffer tube. It looks pretty good and is barely noticeable, but it ruined a very nice Colt buttstock. Comes complete with buffer tube, buffer and spring. $45 delivered
Paypal +3% or money order
Edited to add, only the buttstock is Colt, the rest of the parts are not.