If I drill up a bent blank and buy a kit with the trunion and barrel still in one piece will I need to seperate them and install the trunion and press the barrel in? And if I don't and I install the two together will I need go-no-go gages?And working with rivets is something I do every day at my job (Delta Air Lines) but was thinking of going with the screw method around the trunion.

It's a matter of preference.  When I build, I press the barrel out just far enough to uncover the rivets so they can be knocked out, then slowly press the barrel back in.  If you go slow there is that point when, as you look through the barrel pin hole, that the seam disappears. Then your headspace is back to original spec. You won't have a cant either.  If you take the barrel all the way out you will have an issue getting the pin hole re-aligned. So, DO NOT press it all the way out. You can skip that, but getting the last pieces of rivet out of the trunion, is a pain in the extreme.  Go with the screws all the way.  Screws are better than rivets and you have symmetry.

good enough will do that is what I thought.