If you look at the 4 400 hp @ 6000 rpm 318 builds going around they all where basically a zero decked 318 with 220 ish cfm heads with around 285 110 lsa .500-.550 lift some did it with smaller cams, add 50-100 cfm to the heads should get you up near 500 hp give or take, still probably go air gap unless it's drag only 1 3/4 headers and 750-850 carb. A 400-500 hp 318 in a early a body with 6 speed and some deep gears that handles like a sports car would be a fun car. I'd wouldn't overly worry about 500 hp but go with the Trick Flows, and try to come up with a valve train that would allow you to rev 7000 + rpm and make power, If you could make Rhoades roller lifters with a moderate duration 230-240 cam on a 108/110 Lsa and even use maybe 1.7 rocker to get the lift might come close to an engine that makes near 500 hp and still be decent streetablity. Even a small solid roller might do the trick, when I wanted to build a 400-425 hp 273, the Comp cams solid roller 268 with 230-250 cfm ish heads on my dyno program make a nice flat hp curve from 6000 - 7500 rpm and flat torque through out the powerband even down low, who knows how it would of played out in real life, good thing about smaller displacement engines they don't nose over after peak hp as easy as large displacement.
Now days with cheap turbos is another way to go.
