The function testing I just did got the weapon to run very well last time I took it to the range. It's now ready to add some accessories to the mix.

I purchased some Tango Down SCAR 4 1/8" panels---one for surefire pressure pads, and one without the pocket. The panels have what Tango Down calls binary texture. It's very nice actually and I'm certain that this weapon will handle very efficiently.

The Streamlight TLR-1 has 3 different pressure switches which can basically accomodate any setup from pump shotty to customizeable pocket VFG. In this case, I'm using the 69132 tape switch and a TD scar panel that fits Surefire tape switches. A little bit of dremeling makes for the slight difference in dimensions to work on the panel pocket. I also use double sided carpet tape...blue outer layer and super sticky.

By virtue of luck I suppose I used the YHM Specter LW forearm. The benefit of this rail is that it puts metal where you need it and not where you don't. The gun is a little front-heavy, but that has more to do with the heavy-barrel profile than the rail system. It's still very manageable. I did notice however when putting my pressure pad and scar panel on the rail that I could potentially run the wire in the "channel" between the picatinny "ears" to keep it nice and tidy.
This is where the Magpul XTM panels come in.

The rail panel clips in in 2 points and has a center 'bar' which allows the panel to be locked into a picatinny slot. It's not going forward or backward and it allows the wire to be run under the rail panel. Instant wire chase. The wire then ran out by cutting out some of the interior of the XTM panels so the wire could feed out. I did use 2 zip ties to keep the remaining portion of exposed wire secure so that it would not snag.

For posterity, you need 6 XTM panels to cover the Specter length handguard.

The YHM handguard cap comes with 15/16" ID or 1 1/16" ID and is supplied with a small tube of Loctite 222. It's purple, so be sure to wipe off excess from your black/FDE/Tan/FG/OD beauty....
I like how the forearm cap really completes the look of the rifle. The Loctite 222 starts to setup fairly quickly, so what I did was put a little on the cap's threads itself and a couple drops on the rail system. It threaded in very easily what little excess I had wiped cleanly off within the first few minutes of installation.

Hopefully this will inspire someone as I find solutions that might be beneficial to many coming from building such things as AR pistols.