I just got a great deal on a 20" complete Colt A2 upper.  ($200 for the unfired upper, bolt carrier group, charging handle, four mags, collapsable stock and a fixed stock.  

I am thinking of either keeping it stock and getting a large pin lower, or making a SPR out of it and replacing the upper with a milspec flat top small pin upper.

I guess what I'm after is, how available are the large pin lowers?  If all I'm planning to do is shoot matches with it, I may just opt for the Colt lower, but it bugs me that many of the internal parts aren't interchangable and are not mil spec.  This still looked too good to pass up.

Omar, the large pin lowers are far and away the most prevalent if you go with Colt.  However, they are (I think) exclusively pre-ban so you will pay a handsome price for many of them.  Many of the green label models have the mil-spec fire control parts, no sear block and the large pivot, but these are also among the most expensive.  The SP1 series lowers probably offer the best price if you do not mind the slab sides.  Early blue labels had the large pivot, but do not have the mil-spec fire control pins.  Some of the blue labels had the large pivot, large fire control pins and the A2 features.  The bottom line: it really boils down to how much you want to pay for the lower.

Bushmaster sells a pair of half moons that will make it fit a small pin lower, and are removable if you later acquire a lrge pin lower. Or, if it is a forward assit model, you might want to consider swapping the front end stuff onto a current small pin upper, and selling the large pin job on this web site. From what I hear SP1 owners snap these up.  I did awhile back when I found one at a show [:D]

Two Words----HELL YES

Yeah, I may just unbarrel it and sell off the upper to help amortize the cost of a milspec upper or just get the halfmoon clips.  I don't want to sink money into a preban lower, especially at this point in time.

Thanks guys.