Looking for some suggestions on engineering... I'm building my Granville Bridge on the workbench. It's a custom configuration of the Model Railroad Stoneworks Rockville Bridge kit. Amazingly, the specs are nearly identical (See The Granville Bridge Project).
Half of LEWIS interlocking is situated on top of the bridge deck. Specifically, three sets of crossovers. The bridge is made of Hydrocal. The roadbed is a half inch of Homabed. The issue is control of the turnouts.