Glad to hear you were able to resume the work on your blaster!
As for the trigger, I recently installed what suspiciously looked very similar to the one used for the blaster. It looks exactly like a flip down door stop that has had the rubber foot shaved down to a taper. They mount with 3 screws. Even if that's not what it is, that's what I'm going to use.
Here's an example of what I'm guessing:
http://www.doorware.com/images/products/DHK5-EXT2_525.jpg
As for attaching the 'barrel' to the rear bolt, I think I'm going to use some small screws, since I will have some temporary electronics (pumpkin strobe light) installed and will need to be able to disassemble it down the road. The parts actually are a press-fit so it almost needs no fasteners, however, I'm sure my son will drop it a few times so that it can get that battle-damage look.
Just a thought, though, the coupling looks very similar to what is on a boot for a motorcycle. It connects the carburetor to the engine and also the air box.
What are your plans for attachment?