Wow... a lot of good info flying around today. I will be keeping that ladder safety pdf. I do some consulting, and that is a great summary of ladder safety and use.

Leon, you might want to take a look at the "unistrut" suggestion from OFWW. Check with your local electrical supply house under the name of "Kindorf" since that is the way they sell it. I pay about $60 for a 10' stick, and that would take care of your length. The trolley wheels make that workable for you as you can modify them to be a face mount on your ladder itself.

On the backside of the ladder you could mount a couple of workbench wheels that would allow easy movement of the ladder. Tons of them on Amazon:

https://goo.gl/aydc19

You could mount some wheels to the bottom of your ladder sides, and then put some adhesive in the bearings so they didn't swivel, but rolled freely on a straight line:

https://goo.gl/LLBg0H

You could get these, put rubber feet on the bottom of the sides of the ladder, and lock them up to move the ladder (3/4" lift) and then roll your ladder in place. Again, swivel to straight line rolling and easy cure.

https://goo.gl/GplKkp

If you want an underwire buy 1/4" all thread. HD has it cheap, something like 3 bucks a stick. You can groove the bottom of your steps to receive at least part of the radius (or not) and finish the ends of the all thread with an end cap nut over a washer. Lay out all your hardware and spray paint it the color you want before assembly. If you mortise your steps into the sides (really Robert... it's Leon... it will be dovetail mortised and Dominoed... !!!) then you can assemble with all thread only and no other attachment needed except maybe a high viscosity glue for the end grain (step) to long grain joint above the all thread.

One thing I would certainly do that is cheap and easy would be to build a mock up ladder out of 2X4. That way you can check for clearance, ease of use, step distances and verify your dimensions. You could build a lean to mock up with $10 worth of material, and a nail gun in minutes, knock down after you are happy and use the 2X4 parts for something else.

Love to see what your final decision will be.

Robert