I had this done.....
A friend gave me a Gew. 88...... It had been Bubba'd- heat shield removed (no back sight), barrel hacked off to 18 1/2"...... on firing, primers backed out of the pockets (excessive headspace)........ but the Bubba'D stock sure was purty.......
Fred Ragle of Omaha Gun and Machine fixed it for me. It was not cheap, or easy or quick. But it is fixed. Fred is not the most punctual guy, but he said he could do it for X amount of dollars, and when it turned out to be harder than he thought it was going to be, he figured it out and got it done at the agreed upon price, even if it did take a bit longer than he had planned.
BTW, firing that thing after dark is a hoot, what with the short barrel and loads developed for longer ones...... a rifle and flamethrower all in one!
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."