I am working on a deal to buy the upper. It is an A2 colt with the smaller pivot hole. How much will it cost and how do I remedy this?. Also, I will have to permanently attach the brake and cut off the bayo lug. Will this mean I need to refinish the whole barrel? or upper.? I am wondering if it is worth the hassle or pay more for a post ban.
Thanks for the help? I am kind of a novice yet.

Went through a simila delimma about 6 months ago,only my lower was a pre-ban. I posted a this question and checked out prices.

Was advised by the "experts" on the board to get a new upper instead as the costs would not be that much greater.

You can check with Kurts Kustom Firearms and get a decent extimate on this sort of work.  There is a link to his site on the Industry Communitte Forum. I know I was shocked on how much it would cost to rework my A2.

Thanks Gecko, That is what I was wondering. I was tempted by the A2 preban colt but it isn't worth the extra money and hassle.

you could just machine the dogs off the bayo lug, so that a bayonet couldn't be attached, but still aesthetically pleasing. Then if the ban sunsetted, spot weld some steel back on it and grind them back to original. Whole lot simpler just to replace the whole sight base though.

You can keep the threaded barrel if you attach a screw-on muzzle brake, then drill and pin it, weld over the pinhole; many postban brakes are attached that way. If the ban sunsets, you can mill the brake down to and around the pin, then remove it with pliers, unscrew the muzzle brake, and replace it with a flash hider. It will ruin the brake, but at that point a small loss. At least you wouldn't have to cut threads in the barrel like you would if it was a post ban, if the AW Ban does sunset. Oh, and you can get new pre-ban config uppers, from places like CMMG and model1sales.com

Thanks for the info. I built an STG 58 FAL earlier and if the Ban goes away so will the hassles. I am going the post ban route. Thanks for the input.