70 C10 SWB Frame Measurement Needed

[xr4tic]

Hey all, hoping someone can help here.

I'm in process of installing a Summit frame brace kit and things aren't lining up. I'm trying to figure out if it's the kit or my shortened frame (done by previous owner)

I'm looking for a measurement from the rearmost upper rivet of the front body cab mount and the frontmost upper rivet of the trailing arm crossmember (see pic)

I'm off by 3/16" on one side and 1/4" on the other.

Top pic is from the instructions, bottom pic is what I have. I measure 29 5/16" on one side and 29 3/8" on the other, but my frame holes are 29 1/2" and 29 5/8"

I fear it's the frame because the holes aren't even the same side to side.