-- 5 Compact Track Plans thread was brought back a few days ago about The Chippewa Central. Refer to the article + trackplan in the 2nd reply -- Where its HO Scale benchwork dimensions has three sections (4'x4' + 2'x4' + 4'x4'). So, you you can see how much trackplan can fit into this area.
CR&T's local inspiration for helix portals are the Gallitzin Tunnels. Note this neat 2001 picture of a PRR E8 -- "Same tunnel" in 1965 before new 2-track portal/bridge construction with Horseshoe Curve helpers -- Also note the old steam/smoke blowers, and the AR Tower Wye which is actually a reversing loop for helpers back to Altoona, PA.
My U-shaped (N Scale) CR&T plans a year ago (the 5th reply), was always to use the C.C. to the right of the helix on the lower level, but now -- CR&T will be placed, on the upper level, where its smaller traction radius curves are more effective, plus at eye level. The lower level, formerly the upper level, is still pure Pennsy, suited to larger track radius. Plywood cookie-cutter will be employed to better control grade transitions, and strength for stress from traction poles and overhead wires.
