Frame screws are 10-32 thread, I'm sorry but I don't know what length.
Can't confirm whether it's a juit bolt or not, but it's certainly styled like his gen5 bolts.
Looks like the stock ram, the easy fix to broken down bumpers is getting more of them, they're just about dirt cheap.
The delrin piston will cut down on wear on the internal surface of the LPR and possibly improve recharge due to reduced mass, don't know how much though, it could be negligible.
Be sure to lube everything with DOW55 except for the bolt, which in this case seems oringless, so it doesn't need any kind of lube.
Be sure to read the manual & stickies: http://www.boblongdirect.com/SearchResults.asp?Cat=35