Glad you bought it, (I am a big Colt Fanboy) I have never heard of a SP1 being out of spec and you said it appeared in good shape, so I probably would not spend the extra for him to check it, if it was another brand I could see it, BUT for complete peace of mind 90 bux is not much compared to the price of the gun, the one I bought had been shot probably a moderate amount and as I said it runs fine, no holes out of round or such. It ran fine with the original parts when I got it, but I bought a colt M16 lower parts kit on gunchoker, they are still listed if you are interested. The only thing I found on mine that obviously needed replacing was the gas rings in the bolt. Another reason that I chose to just use the big front hole and other SP1 or A2 uppers is that the colors match, my experience is that newer uppers will be noticeable darker than the sp1 lower....congrats and I hope these damn wait times start down soon. To answer your original question, there is really no down side to owning a converted AR, especially a colt.......except the ammo bill.....
Awesome, I'll probably just pay the 90, whats one more 90
Thanks again, appreciate all the help in this post