I think you need to get a good professional fitting by someone who understands older steel bikes with horizontal top tubes. That Volpe and Albion even look like two different sizes.


As to the Sport SX frame...... the '87 Sport SX was a great bike. I had thousands of miles on mine, including a try at cyclocross, and good crash or two. The DB ChroMo frame with Mangalloy stays may be slightly lighter and better riding than your Shogun.


The fitting of fatter tires may be a trial and error thing. You have the wheelset so stick them on the Sport SX and see if they fit the frame. The stand over it and see how it fits with the bigger tires. Then lay a towel over the top tube and lean on it with your forearms as hard as you can and roll it and see if the tires rub. You may only be able to go up to a x30 b7ut if it is to be fast bike I don't understand why you would want a huge x35 tire.