If you find and buy one keep in mind that there is still a big sheet of hot high speed gasses coming off the front face of the cylinder. So it's held with both hands back on the grip instead of one hand forward like with a regular rifle.
The picture shows that really it's only a set of stocks screwed in place. Since it's restricted either way I'm thinking that you could make up a shoulder stock and fit it in place of the stock handpieces.
This might be fun for giggles for someone that already owns one of the Alfa revolvers. But if you are simply looking for a .357Mag carbine I'd have to suggest one of the clones of the lovely Winchester 1892. To keep it short and compact Rossi makes a 16 inch barrel version. But really the 20 inch balances a bit more nicely with the hand wrapped around the receiver.