that part screws into the breech/firing can ? The part that you unscrew to remove the bolt ? If that's the part, also known as the "rear body" in the parts list, then yes, it's the same one as the Vibe/SP1/G-1/Envy.
The only difference the between the G-1/Sp-1 is the feedneck/barrel/stock/and the board settings and the firing can is milled for eyes. Everything else is the same.