Think of it like this. The SB has the recessed fly wheel and the first clutch disc goes down in to the fly wheel. Machine that outer ridge off flat with the bronze inlay and replace the outer rig with shims where the pressure plate bolts to the fly wheel sp ot can be adjusted. In theory you could take a SB fly wheel to machine shop and have the outer rig machined down to be able to put a few shims on there and you would have some adjustment to tighten them up, say you take .030 off the top replace it with .030 to keep all the tollerences the same in stock form.