Help with First gen Camaro frame alignment

[pollusky]

Good morning, I'll go straight to the question since I'm in the middle of this. I am currently trying to align my 67 frame but seems I can't find good info on how to do it. Some say align the GM holes and measure diagonally, found a video online that said to measure the wheel base. I already align the side reference holes and measure across looks ok but when I measure the wheel base from the rear to the front it is 1 inch off on one side . The only reason I can think is the rear it's not straight or something . Should I leave it like I have it right now and check the diff location or what you guys regimend. Thanks

[pollusky]

Update, right now I checked the rear differential location and it's right on the money. I aligned the frame with the GM aligning holes and cross measure using plumps like detroit speed recommended for my sub frame connectors. Measures the wheel base and came 1/4 off but I'm gonna attribute that to the car not being align tires might be off on the toe