I came across a .pdf called "D&S Designs AK & Semi Auto Receiver Plans and Instructions", dated 2000.
It talks about a couple of caliber conversions for the AK, and mentions that .50 Action Express will feed through a .30 Carbine magazine, which might be easier and cheaper to work with than a Desert Eagle magazine.
Wikipedia says the .30 is 1.65" long and the AE is 1.61", which sounds okay, and since the carbine mags are double stack, the larger diameter shouldn't be a problem either.
The AE is a true .500 like the .500 S&W and the .50 Beowulf. Green Mountain still lists their 15" barrels for $80, which would need a permanent muzzle extension or brake to bring them up to 16".
I didn't find anyone renting a .50 AE reamer. Pacific doesn't list one as a standard size, nor does Manson or Clymer, so you'd be looking at $140-ish for a custom. That might be why I didn't find anything except Desert Eagles chambered in .50 AE.