That tube you're talking about is a part of the A.I.R. (smog) pump system. I've never heard of anyone keeping the smog pump after running LT's. There is a GM pulley replacement for it, if you want to take it off. If you try to run a shorter belt, the belt will throw.
If you run the holley tbi, you might have a hard time running an e.g.r. The t.p.s. sticks out too far, and I had to block off the e.g.r. port for clearance. I'm running a Weiand dual-plane (300-64). Not sure if that would apply to the GM intake.
If you dont do much offroading, I'd go with an LT-4 cam. Run 1.6 rocker arm to get a little more lift. If you can burn your own proms, from what I've read, its an easy cam to tune. Also, you wouldnt need a holley tbi, just a ported/polished 350 tbi with maybe bigger injectors.