1972 Dodge Colt

Hi Stan,
New member here. I build model cars as a hobby and I'm currently doing a mid-70's Pro Stock mid-70's Hardy design (I'll make it in brass btw). I discovered your build and have learned so much from it. My one big question is what diameter are the double main frame rails.........from pics I've found they appear to be about 1 1/4" but in others they appear to be 1 1/2". Your reply would be most welcome.
Thanks in advance,
Codi