I've been doing this for about three years now. My main focus has been Dallas Cowboys sets that include players that never had cards, but recently I've started dabbling with other teams like the Packers, Steelers, and Redskins. They've been a huge hit with collectors! The most satisfying part has been the feedback from former players. Especially the guys that never had a card. Check out my website to see all the sets and singles I've done.
http://www.thecowboysguide.com/RetroCards.html
My latest project is a 1966P (Philadelphia) Final Series 140-card set. It was a huge project that took almost a year, but I'm pretty happy with the final result. Here's a link to that set...
http://www.thecowboysguide.com/Retro...66P-Ser3p.html
You'll find that having them made into 'real' cards isn't as easy as you may think. Feel free to contact me if you'd like to discuss anything.