I used a scrap of 1-1/2" foam and glued a layer of cork on top so I could use "TEE" pins to locate and hold the parts in place while the glue dried. I made the plans on CorelDraw for the bents and taped them down to the foam/cork boards with a sheet of parchment paper over the plans.
For the most part, I just eyeballed the bents and cross braces. This print and MEK made quick work of the bents.
As they are right now, the bents are taller than I need and I will cut them to a closer length once I get the ceiling tile and foam cleared from the area on the layout.
I did much the same thing for the stringer. Instead of making a pair of stringers, I decided to cheat and make only one stringer 3/8"wide. Once I get things painted and assembled, I doubt you'll even be able to see it? Doing it this way made it very easy to shape the pieces and glue them together.
If this bridge would have been positioned up front, towards the edge of the layout, I probably would have opted to use wood, but so far, using styrene, this has been a breeze to build. Once painted and weathered, I think it'll be tough to notice that its styrene and not wood.