Suomi drums may be a PITA to load, but all the war reports say they are extreamly reliable in use. Also those suomi barrles are very accurate by nature. I can see the makings of a very accurate 9mm AK pistol.
A sten kit yields a barrel which is easily sleeved, AND a mag well. I am thinking a sten conversion would be nifty.
Or maybe a hybrid using a suomi barrel and a sten magwell.