My first semi auto rifle ever was a post ban bushy that I purchased when I just turned 18. They didn't have many accessories back then.  After nearly a decade, after few other preban rifles other than AR, I decided get my self another AR.

I wanted my M4 project to be all Colt. It will have all the goodies on it of course. I found a preban 16" A2 Govt carbine for a good price. It has a hinge screw front pin, and what appears to be a sear block. Will this lower fit a newever A3 upper? Since it has a A2 upper, is it fairly easy to swap A2 upper housing with A3 housing while using the old barrel to save cost? Since I plan to use FF RAS, barrel would have to come off anyway. Also, how much should I expect to pay for preban 16" A2 Govt Carbine in an excellent condition?

Thanks for your answers in advance.

Thanks for your replies.