I always come back to this image for the Standard Cornish:
http://www.ansi.okstate.edu/poultry/
I think the image you have in mind of the "perfect" Cornish is more of the British standard for Indian Games, Ryu. Some would say that since the Cornish/Indian Game is an English breed, we should follow their standard, anyway.
I was just looking at an image I have of a 1914 Dark Cornish and I think it matches your breeding goal fairly well, too. An interesting tidbit is that in the 1915 APA Standard, the eye color for Dark Cornish says: "Yellow, approaching pearl."
Looking at the 1929 portrait, the standard type had changed to a shorter-legged, stockier, less-wattled, shorter-beaked, pearl-eyed bird closer to what we see today. Your current exhibition birds are much more squat than this, however.
So I think your goal is rather traditionalistic, actually, which is kinda neat. Your breeding strategy makes perfect sense and I hope you'll keep us posted on your progress. You sound like you're on your way to developing a distinctive strain of your own which leads to diversity within the breed---a very good thing in my book.
The only thing I might suggest is that you find another exhibition-type line which is correct on the issues your current line needs help on and do some experimental crosses with them, too. Crossing lines can really screw up your lacing, but it might be worth a try. It'll certainly net you some hybrid vigor.
After saying how rare Dark Cornish were, I was finally getting around to reading my Poultry Press and there are a slew of DC champions in May's issue. So there's more really good stock out there than I thought...
Cheers and good luck!
TC