Did you remove the clip from the donor or was it already removed? +
simply meaning that it may have been tweaked to begin with if you didn't see the donor vehicle.
I'd measure from set points on the subframe to set points on the frame that are even with each other on both. Meaning holes or spots on each that match on both sides.
This is how my buddy installed a number of Camaro clips on TF trucks. This one was going to be seriously low though. Main thing is that the bottom of the subframe rail is parallel with the bottom of the truck frame rail
https://photobucket.com/u/mr48chev/a...2-85910f302fb5
I figured out that it works best to block your subframe up at it's stock ride height which has the bottom of the center of the crossmember about 6-1/2 inches off the shop floor and have the back legs level on the bottom and then with the truck frame level you block it up at the ride height you want to end up with and then mate the two.