I want more Hp for my 318

I bought a 67 Cuda and love it, except for the lack of power. The car runs great but I think I can take it in my Dodge mini van. It has a beautiful 318 with a Edlebrock Performer manifold, a 670 CFM Holley 4 barrel carb, dual exhaust, 8 3/4 rear end, and a TCI tran. Some day I may drop a new engine in it but for now I would like to install a CAM and/or headers. Does anyone have any thoughts or experience and is this a waste of time and money for a 318? What do you think I will gain, another 75 hp?