Windham could probably market these as a notional "compromise" rifle. Remember, the Army originally saw the M16A2 as totally unsuitable for Army use. They didn't like the 1:7 barrel twist (preferring a 1:9 twist as optimal), the extended stock, the A2 barrel profile, and especially the new rear sight. According to the study they commissioned, the M16A1 was more accurate than the A2 out to 500 meters, more reliable, and the buttstock was more suited to smaller individuals. And (probably worse), the A2 was a Marine initiative.
An alternate history scenario might be: "In 1983 Army and Marine representatives met in the Pentagon to hash out the specifications for an upgraded M16 rifle. In the end, the USMC agreed to let the Army keep the A1 handguards, pistol grip, rear sight, and flash suppressor but went with the new barrel profile, rifling twist, and longer buttstock. This new variant was designated the M16C (for"Compromise")".