Ok so attaching the launcher with the thompson barrel. It's a little tricky but this is the best way. Credit to Kevin Mayo this is his method and it works really freaking well.
First assemble both the thompson reciever with everything accept the barrel. Assemble the launcher with the upper barrel vent and install forend extention bolted or welded in place.
Next install the front of the thompson barrel into the barrel vent tube barrel
Now the forend extetion from the factory is hammered. You will need to polish and clean it up so it slides right in.
Once the barrel extention is partially installed and tge barrel is set up to thread into the reaciever, tighten it down
My direction suck but ill do a video of it being fully assembled from all the individual parts when it's done.
Also made a washer to work better with the stock