I would go with what sets records.
x2
I'm an admitted simpleton... pushrod engines instead of OHC, boost instead of 13:1+ CR,
but many people have had success with the aforementioned engine types. Destroking an
already small stroke SB2 (2.85" stroke for 305ci, 2.43" stroke for 260ci) seems like it would
only find effect over 7,000 rpm, whereas starting with an already "small" 250ci Chevy I-6 or
231ci Ford V-6 (E) , 294ci LS or 302ci Ford (D) and getting your desired CI through a good
bore/stroke combo is the way I'd go. Of course, the ubiquitous destroked 4-bolt SBC seems
to be a crowd favorite, and for good reasons.
Thinking outside of the box is cool, but I don't have the money or engine building experience
to turn those ideas into a fast machine. A 4" bore & 3.6" stroke @ 9:1 CR + boost is my MO.