Main Vent Issues

I want to move the rear main vent farther away from the end of the main. It's just four inches away right now.

In order to do this, I will have to take the existing rear vent out of it's sandwiched position on the main which is between a return and a riser. If I do this, the new rear vent will be about 30" from the end of the main.

The boiler is not new, but even to Keyspan's frustration (they want to sell us a new one), it still hums beautifully.

There are 3" mains piped to the boiler. The front main is a bit more than 25' long and the rear main is just over 35'. I spoke to the people at Gorton and they said I could install the big ones, #2's - - one at each end. I have the #2's and nipples that will raise them 8" high on the main. Can I proceed?

Any advice on how to get the drill filings out of the main after I drill and tap? I have some off Dan Holohan's books on steam, but nothing on this.