300 HP out of a 318, is it possible with bolt ons?

while there's no magic button, there is a fairly easy to follow recipe.

you need compression, you need head flow and you need a not outrageous cam. if you have okay-ish compression and you don't hobble it with a massive duration cam and get some decent heads and 4bbl on there with some headers you're damn near gonna make 300.

if was was undertaking this task with a 318 i'd probably skip used LA heads and go right to magnum/speedmaster/etc or some other aluminum head. factory iron heads are a crap shoot and if you get some that need work-- say seats and valve guides, new springs, etx you're already squarely in aftermarket territory money wise. maybe not brand new aftermarket, but easily some used eddies. the only caveat being if you already had or could score a good deal on some legit ported heads that were already set to run.

everything from there is a compromise. build for torque or look for high RPM power, go single plane and double pumper and shoot for the number or throw a dual plane at it with something a little more conservative on top and cackle wildly as you roast 'em in 2nd.