Sub Frame Connecter Help

I have both subframe connecters, and the cross brace from TCP, and I AM installing them on to my 68 fb, I am having problems with getting both front and back mounting points up high enough to weld on to the subframes. Basiclly the subframes seem to be teter totering, by about 1/8 or so. ( I get the backs in place and tack welded, but then it cause the fronts to drop down, and then I can not get the front to seat well enouigh with out removing the tack welds) The car is a shell, and it being support on the natural weight/suspension points by jack stands. I want to know if any one has add a issuse like this, more so if by doing this will help or hurt some other structural thing. If place another set of jack stand on the ends of the subrames close to the torque boxes, and removed the other jacks from the weight/suspension points in an attempt to allow the weight of the car to get the sub frame to settle into place. I want to know if this could damage anything? I think it would actaully may help since the car is not sagging so to speak in the middle. (one this note the car is very straight and solid and the is little deflection in the door jams). any information would be helpfull.

Where you able to get the Sub Frames Connecters to sit flush on and with the Frame rails?

They fit in place well and line up, but the seem to be cacthing on the floor pans, which i think is why they are teter totering back and forth once you get them into place. I dont have the means to get the car to a frame shop, I dont have wheels that will clear the 03 04 cobra brakes, or other suspension i could put on just to ge is moved. I am going give TCP a call, to see where and how high the mounting put should actaully go, and tell them of my problem. Then possible try and cut slits in the floor boards, to see if i can get the to sit right, since i am replacing the floors any how. thanks for the info