I cant tell you if the dimensions are the same or not. I can tell you even if they are different they are still going to be very close.
I thought the replacement front floor plans are sold as 71-72, the replacement rear floor plans are sold as 71-73 and the trunk pans are sold as 71-73.
You notice you dont see 74 listed? I dont really know why. If memory serves me right Im thinking the 74 small block cars were different but who knows anymore.
Regardless if there is a difference in size its going to be so minor that who ever is building your cage can make up any differences.