Even if you seal up the rims so you can run tubless tires, it can be a problem because you have to do it again after tuning the spokes. The weight difference between the S/M and America is in the rims and second front brake disk/caliper, so the America would weigh nearly the same with cast rims. If you really feel you must go tubeless, I agree with the others that it would be least expensive to get a Speedmaster and fit the America bars and seat. Your dealer might even be talked into giving you a credit/replace deal on the Speedmaster bits you have replaced. Otherwise, you could probably sell them here in the classified section.
