The piece of rail on the right is a new widget from GG&G. It lets you install the rail on a GI handguard without going through the agony of removing the handguard first. Three toggles lock the rail into place with a screwdriver.
The most significant item is the PWS one-piece extruded buffer tube. It does away with the castle nut and instead uses three hex setscrews to apply pressure to the endplate, and lock up the buffer tube tight against the lower receiver. As an added advantage, it has an extended "lip" to prevent the bolt carrier from tilting, something that is supposed to be a common occurrence with piston guns.
Now that I think about it, that may make some sense. Despite the scorn heaped on the M16 gas-impingement system, the hot gas is piped directly into the bolt carrier, with all mechanical forces acting on the centerline of the bore. A piston weapon has a piston, rod, rings, and springs above the bore centerline. If everything is built right, the mechanism is perfectly parallel with the bore, but there is still an unbalanced force pushing back from above, thus making the rear of the carrier tend to "dive". Maybe Gene Stoner had some good ideas, including cutting back on the mass of moving parts.
This is as far as I've gotten. I'm still waiting for the upper receiver, which is the whole reason for the project in the first place. With luck, it will be here some time this week.
Despite my searching, I couldn't find every last pin and spring, so I bought $21 worth of parts from Brownells. Meanwhile, I'll be tuning the trigger parts, and scoping out a new scope. I also ordered another PWS buffer tube. I'll put it on one of my current M4s, which have known accuracy, and see if this new type of tube can increase accuracy. I was impressed with the solid feel of everything as I put it together, so it's worth my while to test this tube on another rifle.
Overall, this buffer tube looks like one of those ideas that should have been adopted 40 years ago. It's easier to install, seems more solid, and has other neat features. It is, however, considerably more expensive than the dirt-cheap generic parts out there. I hope it's worth the extra cost. Only testing will tell.