I have never owned a Nelson 36, and I've done OK for myself. To answer your questions in order:
*Placing the bellcrank pivot behind the CG makes the line slider sweep back positively without the need for a spring, rubberband, etc. It only matters during the split second when the line slider is in transit. Otherwise, where the bellcrank is mounted doesn't matter. (Don't let anyone tell you otherwise!)
*My profile MO-1 has 345 sq. inches of area. If it weren't so windy in Texas, I might go as much as about 400 sq. in.
*My wingspan is 44". I made my profile, Class I and Class II all the same size, and 44" is the maximum in the scale classes.
* My wing has a symmetrical airfoil, 12% thick at the root and 15% at the tip. Without measuring, I don't remember the actual thickness measurements.
*I think reverse rotation is helpful for low speed, but not a necessity. I think Fox 36's with the big back plate would be a good place to start. There were reverse cranks made for the Mk 6 and Mk 7 combat specials, so you may be able to get your hands on one of those. Failing that, the 36/40 Deluxe also has a factory reverse crank available. At 1/2", it is a smaller crank than the combat engines. Still, with some work, and perhaps an aftermarket piston/cyl/head button, you can end up with a potent engine. With any of the Foxes, you will want to adapt some other better carburetor. Back in the early 1990's, I wrote an article on how to modify a Fox case to accept an OS carb.
*Profiles don't have to be scale to enter, only to receive bonus points. Whether a CD would give you bonus points for a mid-wing rendition of a low wing airplane is up to the CD. Personally, I probably would not give bonus points.
I have plans for my profile MO-1. I can provide them as a PDF or paper copies.
*My profiles typically weigh about 40 oz. I can build them lighter, but they can be too light to fly well in the wind. I actually ADD weight sometimes if it's windy on contest day.
I hope you find some part of this useful. Best of luck to you.
Bill Bischoff