i just ran 13.9's with a 100% factory stock block 318 with about common factory 340 parts. cast intake, about same cam, 3.55's, still 318 heads but headers and a little better stall. street tires.
It's just drives me nuts how people act like getting performance out of a 273/318 or 383 or whatever gonna be this crazy extra hard endeavor, like the laws of physics stops under a 4" bore sbm or a 4.32" bbm.
Say you put a set of J heads with 9:1, 650 airgap, headers and xe268h cam with the appropriate stall and gears for best 1/4 mile time for each, 273, 318, 340, 360 there all gonna perform decently not say there gonna do the exactly same 1/4 mile times but doubt there gonna be super crazily apart.