Small update - the body of the muzzle device is looking pretty dang awesome, but the head still needs major adjustment (way too square, need to round off all the edges). Got nothing done yesterday (a good rest), but still did some hypothesizing.
So the handguard sections are going to dovetail together somehow. Just like a scene in the latest eps of Fett, I'd like it to be a 3-piece takedown design, where I can pull it all off if I need to.
The first piece I think I'll design to nest into the rear handguard retaining ring (still featured on the stripped beebee gun pictured above), then pivot slightly to "lock" against the trigger pack takedown pin (very proud head on that pin, will make a perfect locking lug), and also lock into the front end of the magazine well. This creates both a rear- and front- facing bind, which should be pretty secure. This will be easily done with some slight bump-outs on the model; doesn't need anything too crazy.
The immense squared metal "trigger guard" piece will get a slot in the grip area, and will then slot into the rear handguard piece and pivot upward as the rear handguard "locks" onto the aforementioned pin and mag well spot. This should cause a leaf spring forward pressure that should keep everything locked up on the front of the mag well.
Though, if I put too much emphasis into the front of the mag well area, I'll end up blocking the beebee feed that I'd like to keep around for airsoft firing purposes (best way to cue up a blaster effect, imho, just sux this thing isn't semi-auto).... As for beebee feed and functionality, I might build a simple gravity hopper into the top of the rear handguard piece, and have a small brass journal feeding into the original chamber feed area. Probs going to have to heavily modify the underlying rifle to get it to work, but that's my hope at least...
For the scope install, I'm definitely going to do Magpul MOE hardware, as it would seem to distribute the weight the best over the pot metal dust cover (if you move it, it will crumble, etc).... Pretty sure I'll be building a small plate under the MOE hardware, too, to better distribute the weight up top (dear Star Wars: There's a reason there's a side rail on Soviet weapons...). 
Etc...
