Correcting Main Vents

I'm looking to correct a main vent issue on my system. There is currently one small vent at the main's connection to the return on each main. This vent (see first picture) sits on a 1/4 nipple and a hodgepodge of bushings and couplers.

Each main is 30 feet long, 2" pipe. Reading through other posts on this forum, it seems as though two Gorton #1 vents per main should be sufficient. Do I need more than two per main? There are plugged tees (see second picture) about 18-24" from the end of each main that I thought would be an ideal place for the new main vents on an antler.

I think the plugs were originally installed in '95, when the entire system was split into two separate systems. It's a two family, so one of the previous owners separated the second floor from the first floor around that time. How should I tackle removing those plugs? They're 1 1/2", so I'm not sure what size pipe wrench I should be using. Since they've been sitting so long and have also been painted, I was going to clean up the visible threads with a pick and hit them with some PB Blaster before attempting to remove.

Also, What's the best way to attach the antler at those locations so it's sitting vertical?