I think you should go back stock. The hood looks like a Ecklers to me. That is a '69 427 L-88 style center on a stock 64 hood. I had one just like it on a 63 that I raced in SCCA. I am not trying to hurt your feelings but, I think you would find it would not bring big money as a custom even with the questionable Motion parts link.
Unless you can find positive proof via bills of sale for the parts and/or Motion's own body shop having done the work it would not in my opinion be considered a true motion car. One other way would be old pic from that era showing it customized and that date back then.
I hope that someone on here will step forward and say that they reconize it from years ago. You may have a hard road to go with it if someone doesn't come along.
Hope you don't mind the frank words. There are so many guys come on here wanting so bad to have a MOTION car in some way. We tend to be a little hard nosed with out good paperwork or other proof. I hope you understand? Nothing personal intended or infered for sure.
No mater what you decide I want you to know that it could be a neat looking car as a custom. You have some big $$$$ ahead of you either way you go. Let me wish you the best of luck which ever you decide. Don't get discouraged and Keep us informed on your progress either way.
Pantera