I've said before the small block cylinder head is a superior (roughly 10 years later) and more efficient design; for a conventional 440 big block to have the same port and valve area to displacement ratio as a conventional 340 small block, they would have come from the factory with about a 2.19" intake valve and nearly max wedge size ports....not to mention still without the superior valve angle and valves that open on the bore centerline. I always wondered why someone didn't just "scale-up" the the small block head design and adapt it to the B/RB deck....besides needing different valve notches, how hard could that be? not to mention the B/RB has a much better lifter bore angle than the WTF 59 degree of the small block.

As a result, with aftermarket heads It's easier to hit 1.5hp per cube with a small block but that only gets you so far becuase there's a practical limit to the cubes (roughly 475" is the "practical" limit) with a 4.22" bore and 4.25" stroke. An RB big block Mega can go "easily" to 572 or even 605-ish with a raised cam tunnel but becuse of the limits of the Shallow wedge heads (assuming a streetable CR max) it's not always the best bang for the buck.

Also the packaging for a BB is an issue, it's really only practical to consider an A body for mid nines, the big block adds all the weight on the nose and (unless you run a glide) the 727 adds weight too.

When I sum it all up the best 'prctical" (ie, trying to do it on a reasonable budget) mid nine combo to me that would still be streetable would be an R block 460-ish motor with max ported w5's in a sub 2800 pound 67-68 A body notch with a race prepped low gear set 904 and about a 4.30 gear. Second place would be a 511 low deck with B1's or max ported -1's. both motors would have a tight lobe center roller with about 275 @.050 and .670-ish lift on a 12:1 short block with an oversized cooling system. both would have a 'tight' 8" vert with ~4800 stall/5500 flash...it's really tough to hook a 5500 stall on any type of true street tire no matter how well the combo hooks. And as far as the hook the small block is going to have a huge built-in 60' advantage but I think a well tuned BB could just about make that up by high gear with the right guy picking the parts. You can go bigger on the cams and more stall etc but for most people you'd be wrenching on it all the time and it would really just be a race car you're driving on the street.

My 380cfm Chapman CNC max wedge headed 517 was once destined for a 760-ish HP 9.70-ish 67 A body, but my plans got diverted and the motro got detuned to right around 710 but with a massively broad street torque curve to move a 3750 pound B body with 3.54:1 gears.

That said you realize how easy a streetable low 10 combination is by simply scaling down the cubes, block and heads,

Btw....aren't HEMI's Big blocks??

Chip's 9 second 572 is street driven and one of the most impressive cars I've ever seen in terms of drag strip performance and REAL street manners. Put that combo in a much lighter A body and there you go.