A good place to get some clues/ideas would be from Carls Ford Parts.
http://www.carlsfordparts.com/main.html
Every now and then I check to see what the value of High Riser parts are. When High Riser parts (intake, heads, etc.) do come up for sale they sell very quickly. I would expect the tunnel port stuff to be the same way, but how to market it is the problem.