Quick update with the brace on... Based on current "13.5" max from brace end to trigger face" rule I had to block off two positions on the tube, this is longest legal setting based on estimated trigger position. Trigger pack and front end still to-do.

Red section is part of the grip beavertail I need to Dremel off before I can tighten down the back-end screw holding the adapter-chassis-grip assembly together.

Based on this prototype setup, I'm thinking see if Midwest's planned QD STAP cuts enough length to allow Position 5, but stick with the "standard STAP on QD rider" to help keep the length in rifle mode over 26".