Looking for specs/measurements for the front frame rails for a 74 Challenger. Does anyone have the measurements? If so, where is the initial measuring point to determine if the front frame rails are in the proper location and "true" in their placement. What is the distance between the front frame rails? How is this measured? I need to check the squareness of my front frame to help in some front end rebuild issues. Or, should I check the over all square of my entire cars frame rails? I'm not a body guy but want to see if I can check some initial measurements to see if my frame is square. As always,,,,a big THANKS.

It takes some specialized measuring equipment to accurately measure a vehicle, that being said, I don't know if there are known data sheets available for our cars.
You can take x measurements and length mearsurements and compare from side to side. They should be equal or close to, but as far as heigth measurements , difficult to determine unless the car is mounted level on a known level surface. Frame rail width, if it is off , there should de some visual indicators(wrinkles, buckles, popped spot welds, welded flanges not laying flat, etc) on the rad support

You haven't stated what the rebuild issue is , that might narrow the issue down