65 Valiant

I picked up the last car of 4 I bought this spring. The car is a Signet V-8/ auto, convertible. It has no motor or trans. As I was loading it I noticed it had a 5-6" notch made into the rear valance on the drivers side. I looked it over and it is factory made into the valance and has a bracket mount on the frame rail. All the other V-8 cars do not have
this notch. Could this indicate a resonator exhaust was factory on this car and what option packages could you get this in? I inspected the valance and it is factory installed and has no indications of ever being welded on as a replacement. The inner fender tag is missing and I am hoping it is in with all the parts buckets I got with the car. There are no rear seats so no build sheet. Please help.