Youre doing a fine job... cut out some of the 2x10 on the floor and take out all the concrete around the trap. All you need to do is chisel back far enough to cut the trap off and get a fitting on the pipe. That shouldnt be underneath that beam. Looks like your working in the footer or an overpour area for that beam... I thought I was the only one with luck like that...lol Keep going, success is within reach. Just like Hackney said, make a big hole, get some room to work!