No subframe connectors. The stands are on the frame rail in front of the torsion bar xmember. Probably doesn't matter but the rear axle is on stands too.
it's possible that the frame has got enough flex in it that it's causing you issues.
also, motor plate makes me think it was making big dumb power so you might have a twist going on. the K was just holding it all steady and when you removed it all the magic got let out and ain't no way it's going back.
i used to run a 4dr dart with a 440 and no subframes and it pretzeled up the frame enough the the right rear door wouldn't open. and that was on standard soft mounts with and absolutely rock solid west coast car.
i'm not saying this is the problem, but it could be a contributing factor. my money is still on something K related or the arm is janky.