318 cam

I've been doing it for 50 years. It is easy and not a secret. See post #17, #48, and #56. What was factory 340 hp, 275? What times did they run, low 14's? Looks like it is doable... I used to take a pair of milled rebuilt 360 heads, drop a 340 cam, springs, double roller timing set, high pressure oil pump relief spring, a windage tray, a hardened tip oil pump shaft, 340/360 4 barrel intake and rebuilt 340 carb that others were swapping for a slower combination, a Direct Connection electronic conversion kit for around $100, and 360 or 340 exhaust manifolds with dual exhaust. You think that combination would not run with a 340? And what's more, it works with a 273 or 360. Add a custom cam and add "64-67" 273 rockers, and you are now faster than a 340. One can do a lot better than stock 318 performance with just a different cam and valve springs with no dependability problems.
exactly this.

if you're not trying to shoot the moon, you can build a reliable, stout 318 that will absolutely run with the pack. the combo isn't some super secret mix of high dollar and proprietary parts. heads, cam, and a little compression is really all it takes.

it's been proven several times over that you can easily and reliably make a rip snorting 318. can you make more and do it easier with a 340 or 360? sure, that's just basic fundamentals.

and i can already hear the mewling from the great unwashed massed: wHaT aBoUt vAlvE sHrOuDiNg?!?! Durrr rOd rAtIoS mAtTeR!! sMaLl pOrTs wOn'T sUpPoRt hOrSePowErrr!!

honestly, it doesn't matter at these power levels. you're not building a super stock motor. knock that **** together with decent stuff, size the cam and carb appropriately, gear it right and ship it. it'll be plenty good enough to do a burn out in your ice cream cruiser and probably run 13's at the track.