Have you moved forward with this project?
I decided the 820 was not for me and went back to riding my 700c Devil for awhile and then bought a 1993 Rockhopper frameset to make into a single-speed. I rode that for a few weeks and then realized that the head tube of the Rockhopper was just slightly longer than the head tube of my 730. So, I pulled the fork off the Rockhopper, stuck in on the 730, added about a cm of spacers and locked down the headset. I then put my 2.15" Big Apple shod 26" wheels back on, installed a V-brake on the front and my 730 26" conversion is all I've ridden since.
I've decided that the key factor for me is the very low bottom bracket. The Rockhopper is an excellent handling bike but the high bottom bracket and the long top-tube bothered me. The converted 730 fixes both issues. Long-term, I will either further update this bike to have rear brakes (either new canti-studs or a roller brake rear wheel) or commission a custom that is very similar to the 730 (Co-Motion Pangea and R&E UTB are top of the list).
The only issue I would warn you about is bottom bracket height. My 730 has about 60mm of drop and it works fine with 55mm Big Apples. The bottom bracket height is in the mid-to-high 27cm range. Co-Motion's Pangea has 55mm of drop and comes with much smaller tires and a BB height in the 26 cm range and that's an all-terrain bike.
Right now I'm running the 730 as a 1x7 (have a triple but no front derailleur...just been to lazy to remove the outer and inner rings) and will upgrade to a 1x9 when I have a custom wheel built. Simple friction thumb shifter for now and a Deore trigger shifter when I go 9-speed.
Good luck on your project and keep us informed!
Here's mine as I'm currently riding it:
