Help needed with frame to cab mount brackets 69 cab on 65 frame

[tranz am]

I have another frame to measure of off but its currently in use, and a little more difficult to measure being that the holes are still plug welded and the mount brackets are in the way . I might be able to make some sort of jig to measure the dottom holes from front to back, being I am pretty sure the front holes are in the same location on both frames.

I am building this frame on the side until its ready for the 69 body/cab swap. I want my truck to be mobile as long as it can be.