3D printers are great for finding the little tweaks needed. The drum cam and index plate will be steel as will the forks but this lets me try it all out before committing to metal. The shift plate with pawls goes over the index plate and pushes against the lobes to rotate. The index plunger is a ball here but it will be a roller. If you look closely you can see the wear mark of the ball on the edge of the index plate. The same problem all the stock index plungers have. A roller will not make the indent.
I am thinking of adding three tapped holes to the door so a puller plate can be attached to remove it from the case. Generally you have to pound on the mainshaft with a plastic hammer to get it off the studs.
Yes, it actually fits inside the gearbox without modification.