I agree, I'm fairly certain that the only
practical .45acp magazine that really works in an AR style rifle is the grease gun mag. But since they are too wide to fit in a standard AR15 magwell, you should definately get a dedicated lower specifically for this magazine / caliber.
I'm certainly not bad mouthing the other offerings previously mentioned, but I'm glad I went with the CNC Guns/Khalan Weaponry AR45 lower. Other than the mag release (which is included and works the normal way), everything used is standard off-the-shelf AR stuff. The Grease Gun mags don't need to be modified, and you have your choice of the same buttstocks, grips, forends, parts, etc... that we all know and love.
A complete Olympic upper will slap right on, or better yet, have Tangochaser build you something truly special.
Like NH-Handgunner said, since these are all brand new, the only drawback right now is the lowers aren't sitting on the shelf ready for purchase. They are "cooked to order". So enjoy an appetizer and a cocktail at the bar while the chef prepares your meal. Mine is delicious! Bon Appetit !!!