Have a question regarding the very early Colt carriers. If memory serves, the early carriers were smooth sided (no forward assist notches)and were "heavier" in the back than the newer semi carriers but not as heavy as the M-16 carrier. Does anyone know what that dimension is so I can properly identify if a carrier is original?

You are absolutely correct in your description. Colt took M16 carriers and milled off, from the sear trip surface, apprx. 1/4-3/8". Not too much. They left the ramped section where the hammer rides on the underside. Also they should have the classic "C" roll stamped on the left side. I have collected these over the years and have only seen 1 barreled upper with a smooth sided carrier without the mark and I was not able to determine if it was original.