Here's a simplified rear filler sized for the sgn-9 tube of 1-1/4". Its made from 1/8"x1-1/4" steel strap/bar, 3/8" inside wide/tall channel steel and a section of 1/2"x3/8" bar. There is a 0.102" thick magazine stop at the top of the mag lug slot to prevent the mag from being inserted too far up into the gun. It uses the same style of flapper mag catch as the suomi and a suomi one will fit. I'll get the mag catch drawing up in the next few days. The 3/8" inside steel channel is welded to the 1/8" top piece after the .295" mag slot is cut into it. You will need to use spacers to locate the mag catch in the center of the slot or make your mag catch wider than a suomi and narrow the top to fit inside the slot in the top piece as it will have a slight lip to it. The bottem 3/8" steel bar "fence" then can be soldered or welded to the 3/8" channel and contoured to allow some space between the "fence" and the mag catch. If you don't care about the fence, then you can simply leave it off.