Yes I was just going to recommend them clips. Very useful on a V2 box as the trigger likes to pop out aswell.
Yea as said above, just take your time on the gearbox. There is no rush. You will only end up having to strip the entire gun again if a problem arises. Been there so many times
Just double check with the new sector gear and delay chip that the tappet plate pulls back far enough to load a BB and far enough forward to seal against the bucking.
I find MP5 to have small tolerances when it comes to this. If your running a full stroke then timing will not be an issue.
There are guides online that walk you through this. Might be related to Short stroking but still relevant information