Lol!
Says the guy whose car is literally the one that's repeatedly bested coil over converted Mopars. And 3-series Beemers on the same track with the same driver.
Them:
"Better handling! Superior geometry!"
Hotchkis Tax: *exists*
Them:
Looses mightily to a 4 door B body with torsion bars, a big block and power steering
Uh, well the faster lap times he asked about would be a step in the right direction. Some event wins over proven torsion bar competitors?
Geometry maps can show improved geometry, but unless the geometry is dramatically better even that doesn't necessarily mean the car handles better overall.
Calling a ~30 lb weight loss a "handling advantage" is a bit of a stretch. I mean, sure it might help but so can a relocated battery. Or aluminum heads. Or putting the driver on a diet. Have we scaled all the torsion bar cars that were faster than coil over converted cars? Were they lighter or heavier? I mean, if a fully RMS equipped Duster loses to a 4 door B-body I don't think the 30 lbs off the front helped much. Especially since that B-body had factory power steering, just on steering it was a lot more than 30lbs heavier.
Have you calculated and compared the CG to a torsion bar car with the same engine? The engine goes lower, the spring go higher, and a lot of that would depend on the engine choice and components.
How much wider can the HDK go from a factory 73+ disk brake track? I mean, the hub to hub on my Duster is about 61 1/4" by the math. My track is about 58.5", that being the c-c of my 275/35/18's. Going narrower can absolutely hurt suspension geometry. Going wider can improve it, but, you have to fit the wheels in the fenders still. My 18x9's are at a +35 offset already, and I rolled my fenders to clear those. So you're gonna run +45 offsets up front? More?
As for fitting more tire, well, not really. With the torsion bar set up if you commit to 18" diameter wheels and run a "V" shaped UCA none of the suspension clearance is an issue anymore. It's frame rails and fenders. At that point, changing the hub to hub on the suspension only changes the offset you need to fit the wheel in the well. I've been told with the coil over conversions 17's will fit with a large backspace where on a torsion bar set up 17" and smaller diameters are tie rod clearance limited, but honestly for any of these road or autoX competitions the 18" wheels have better tire options anyway.