That thing just screams for a rigid conversion. Don't believe all the negative hype, I grew up on factory rigid Harley Big Twins and Indians. Once you learn the "wash out" angle on the rear wheel you can ride circles around a squish tail. Just takes practice, a sprung seat and a kidney belt. They also do a better job launching from stoplights.
Just for shits and giggles I swapped the shocks from my Suzuki Savage barhopper onto my wife's 800 Intruder. Dropped the back of her bike at least four inches. I sat on the pillion, at 50 mph on a washboard road and there weren't any issues. If I recall correctly, that is 10.5" eye to eye instead of 12.5 or 13" eye to eye. 2 to 3 inch shorter shocks aren't an issue, just stiffen up the setting a couple notches. I'd go measure the shocks but the Savage isn't at the house, the Intruder shocks are now on it, no more scraping my rear fender on speed bumps. Semi-floating HD FLH Shovel fenders and short shocks don't mix well.
Take your time and have fun building it.