No clue. You might check the adventure riders or badweb forums. I'd think the stock suspension would be adequate unless you get crazy off road.
Re off-road, seems to me a tuber is not the ideal set up at all for going off-road. With the engine suspended as opposed to supported by the frame from beneath, motor mounts and isolators bear that weight and I suspect you'll be wearing them out and/or breaking them.
I do know if you pump the $$ into a top notch suspension for that application, you'll have a whole lot more into it than the bike's worth. Why go to all the trouble and still end up with something not ideal when you can buy one ready-made for about the same money?
Also - I have a near-stock '00 M2 and IMO, they're a classic. You sure you want to hack one up in the condition you describe?
So, all this unasked-for input aside... I think a V-twin off-roader would be cool! I'd be looking into having a good, chrome moly frame and alum swingarm made. Add lightweight wheels, axles, bars, trees, plastic fenders, etc. Then I'd research the suspension and go with whatever is strong and light. Almost any Sportster or Buell motor would be a good foundation and I'd be lightening it all I could. Figure out how to run without a battery, go kick-start if that's even do-able.
Black, chrome & loud.