[dana44]

This is going to be a fun one, but if you look at the construction, there is also metal bracing on the inside of the rails so it will be near impossible to get behind it to weld and I even think the rail itself is part of this bracing, so, if you are going to replace the rails it is going to be a matter of locating another set, or, get any rails and bend them appropriately, try to have an inch of metal above the rail so you don't have to weld in or too close to the rail, and as much meterial as possible to keep the welding beads below the rail as possible. The top side of the rail gulley is filled with a rubberized sealer, not just painted, so they last longer.

 

[dana44]

Do a serious look at how it attaches to the structure. I think it is actually two pieces squished together. Two L shapes, one laying inside the other, the other folded over to form an edge. The long sides then go into the cab and the top comes down and attaches to it, the long side then becomes part of a support to the inside metal. I would check the looks of it, replace in sections vice the whole thing at once, grind/cut the old one off smooth first, use the replacement rail by welding about an inch of the sheetmetal above and below and outside edge of the rail to stay away from filling that rail with weld, grind/file smooth as necessary to get it in place. It isn't going to be a five minute job by any means, but I think you will be much happier than trying to replace the whole thing at once or removing it totally, even though that would be the easiest way to fix the problem, I agree it just wouldn't look right.