Well, my search for a flat top large hole upper has brought me to Daniel Defense.  Not even Colt makes them.

Has anyone tried these?  How is the quality and is it really a drop part?

http://www.danieldefence.com/store/cart.asp?catid=1

I have one on my SP1 Conversion and it looks great, and runs like a top.  It did not "Drop In" and required the removal of metal from the butt end and underside of the upper receiver.  If my memory serves me, there are Les Baer uppers with tight tolerances and as such may need to be fitted to the lower.  Drop me an email if you want me to mail you a photo

FNGFROMGA out !

Also, Colt has made a few large pivot flattop rifles in the past and Armalite made a few large pivot uppers.  Both of these are about as common as hens teeth but you can find one if you look hard and long...

Good Luck!

I used a older Colt 6700 since I wanted a large hole flat top that matched my lower Colt gray.  DD used to use Les Baer forgings to make the large holes with, but now they source them themselves.  Those I know of after the change over have not had to fit them, but if you did, it would be minor.  Unless you want to camp out looking for a large hole Colt (and I guess Armalite) to pop up for sale, like I did, go for the DD - you don't have much choice.

I also have a factory COLT large hole flat top upper I bought off of a guy on the boards.  It has a heavy barrel. It sits in my safe, unused.  It does not want to pop into my SP1 Coversion.  I looks like the sear relief needs to be milled out.  It is in great shape so I do not want to machine it. When I get more funds, I will probably get a preban SP1 lower and slap it on that

FNGfromGA out!