Back in 1984 +- I needed to set parameters and design my kidney shaped helix. I had first established a layout room foot print. My grade and passing track parameters included ten cars plus a caboose pulled by Westside or PFM k27s. I knew the 'diameter' of my 'helix'. I used a seven foot long test track and a level. I used whatever to shim up the test track to hit the max grade my test train could pull. Next I used a piece of wood with my dumb 2' level attached loosely with rubber bands. I shimmed up the level to be used to determine the rise per 2 feet. I again used my handy Public School education to calculate the curve compensation (WAG method) for the grade. Given the length of the 'helix' and the rise I needed to achieve I arrived at 2.5 percent. Of course the level laid on the curve is a shorter distance than the actual road bed so the curves are less steep than the straight sections. I laid the first lap with the level and the rest measured on the risers (to preserve any errors). I tested as I went and my 'back yard' engineering held up.
When the Blackstone K27s arrived they were a bit 'slippery' compared to the Westside engines. I can't recall the weight comparison? At the time I wondered if the wheel plating or the tread profile or the weight made the difference?
My lame assed strategy (as usual) is to mock up and vary the variables. Go ahead, live dangerously. Spike a couple of pieces of flex track down on a 1x4, get out some equipment, run it and take measurements.
In the mean time, Later this afternoon I may go over to Apache Reclaimation to check out their stock of surplus Rail Gun components.