That wiki chart is my buddy
Consider adding a little geometry for the Delta Ring. I think it'll help sell the A2 hand-guards better because it looks sort of like a free-float tube at the moment. A rear sight aperture would be nice too. Otherwise looking like you're headed in the right direction.
Keep at it and have fun with shaders.
(I've read in the many disputes over the validity of the A3 and there are some confusing factors so don't feel bad about it, Keith. AFIK, there were no rifles issued with "M16A3" marked on the lowers. They were either marked "M16A2E3" or made by using M4A1 lowers with M16A2 uppers. For some time, Colt marketed their flattop upper as an "A3" upper which has also leads to confusion. Colt's RO646 (aka M16A3) is primarily marketed to LEO agencies.
So, while yes, "A3" models exist, there is some debate over whether or not any rifles have ever been roll-marked as "M16A3".)