Take a look at these C2Cfabrication floor pans...

Mine is a 70 but I always thought it's the same truck as a 71
well you can see the pictures and the last post of the thread that I just mentioned and see if that looks like yours? Or if you want to go through pages and pages I did them in a 76 Truck which is the same thing for my son in a thread called more purposeful truck under General discussion..
I always thought 71 and older was different..