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I haven't yet done that exact exercise myself....though it appears if one is able to line up the tops of the two different profile rails....and solder them together....that would likely be successful. You might need a short section of code 80 track extending out from both sides of the bridge to have good access for soldering the short and tall rails to each other. Then use a jewelers file to smooth out any rough spots left from excess solder or slight mis-alignment. They say it's a good idea to remove a few ties from each section of track to be soldered.....one reason is they would be melted from the heat. The ties can be glued back in place under the rails after all is done.
Another possibilty would be scratch building bridges from balsa or basswood.
There are code 55 bridges you must be looking at old stock. There is at least two different code 55 bridge kits, truss and girder plate. They are easy to assemble. I haven't seen finished code 55 bridges yet.
On most Atlas bridges, the track snaps off the bridge pretty easily......I have several that the bridge keeps falling off the track. There are just a couple of plastic snaps. I haven't used code 55 track, so I'm not sure if it would snap on in place of the code 55, but a little glue will fix that.