I can't tell you the exact size differences internally between the standard case and the big bore case because I don't know that
I was ask to inspect and tear down a street driven blown BB(454 C.i.) Chevy years ago, it had a small bore BDS blower on it with two Holley 650 D.p. carsb on it. I had called BDS to find out what is was and I was told off the information they ask about it that it was a small bore 6:71
That motor made 620 HP at 5 lbs boost on CA pump swill back in the late 1990s, I hopped it up some, cam change, pulley change and carb. size change and got 780 HP out of it with 7 lbs of boost, NOT GOOD
I built and dyno tuned a blown 484 C.I. gen 2 Hemi with dual 1050 CFM Dominator carbs. with a Littlefield 10:71 blower, that motor made 920 HP on CA pump swill at 7300 RPM with 7 lbs of boost It made 1027 HP at 6500 RPM with 12 lbs boost on race gas going into detonation If you could mount and safely use (clear the distributor or run a crank trigger ignition)a 8:71 on your motor that would be better than the smaller 6:71 )
You can turn the bigger blower slower to make the same amount of boost with cooler manifold inlet temps. which will make more power due to the cooler denser air with more fuel mixed in it