That is a great idea! I haven't ever seen plans for a 22lr sten, but I'm sure you could adapt something like the sgn-22 plans to make a sten. You'd have to make the bolt a semi auto bolt and not the self ejecting single shot like the sgn-22 design. Getting a sten kit would gain you a stock, lower receiver and receiver cover. You could sell the bolt barrel and magwell to offset your costs. You could use a ar15 hammer, trigger, and sear for a fire control group.