I don’t think the previous takes should be useless. If you have your character characterized in a t-pose somewhere on one take, you should still be able to merge import your motion data and it should fit in correctly. I did a similar thing with some Mixamo animations, where you will not find a t-pose either. After trying to match up my character in a t-pose for a long time, i finally got it to turn green all over, and after saving that, i could import merge any animation in on that character. I then have a different character that has the skeleton names that i need for my game engine (in this case, ue4), i have that ue4-character set to be driven by the mocap character and then plot to rig and skeleton from there on. Not sure this was what you meant, but in case it was, hope it helps.