Goat-
I think you’ll find it easier to cut and pull rails out than installing new. Only replacing rails? Hmm.
RE The “drawings” for the job. What does the rail schedule show? 3’-5” starter, but then what?
I’d imagine with a DW and its limited load capacities, 8 footers would be fine as long as you don’t end up with a fish plate right at the bracket, but what does the plan call for? Are 8lb rails on the schedule, or 15lb?
If the drawing you have is the “approved plan”, you’re kind of stuck with what it calls out for unless reviewed and re approved.
But here are a couple of my thoughts.;
How many stops and what’s the rise? Not knowing the structure you’re going to be tackling (oil platform?), is there a chance of going through the DW roof if it’s accessible? Or cutting approx 13’ high through a side wall to create an entrance point for the 16’s or 8’s? (And to remove the old rails).
Kind of tough to survey the job, being 180 miles out to the (proposed) Gulf of America.