Dr, I started a thread on bikeforums where I've gotten great info in the past. I asked if anyone knew the narrowest tire you can run. Matrix rims appear to be made by Trek/Bontrager but I can't find much info very quickly. We'll see what responses we get.

Your best option is probably going to be narrower tires. As I thought about this whole thing I realized that you've got more than drivetrain incompatibility with your old road bike. The spacing of the rear hub on your Trek is 135mm. The old faithful roadie is probably 126 or less. This is a no go. You might luck into a set of cheap wheelsets on Nashbar or Performance but you must have 700c wheels with a 135 rear hub, an unusual combination for after market wheelsets. Usually only comes as OEM but you never know. Search eBay, ask your bike shop, post on bikeforums, etc. I'll go do a few searches also.