The ACT HD is rated to about 420 ft-lbs at the crank, which translates to about 336 ft-lbs at the wheels. I think a Stage 2 setup yield somewhere in the area of 240-275 ft-lbs, depending on the dyno... at least that's what I got from searching a bit.
Here's a bit of a comparison for reference:
According to that, a 20G will put you just over the limit of the ACT if you're running E85. Also, I would expect that it can probably still hold up fine if you don't abuse it and especially on 91/93 instead of E85. But personally
, I'd get something that holds more torque if I were going with a 20G only because I like having an extra margin of safety.