A-Body differences

Just bought a Dart floor pan, rocker to rocker and rear seat perches up to the front, almost to the crossmember and low and behold, it's longer than the '69 Valiant it's going into!

I guess my '69 Valiant has the 108" wheelbase and a Dart has the 111" right? It seems, upon initial inspection and measuring, that the extra 3" is right behind the rear pans, or right in front of the hump up to the rear seaT (however you prefer to reference it). We're thinking we can just cut this little extra out.....