Take the forged crank and adjustable rockers from the 273 and throw them in a 318 for a lot less money and go faster :D :burnout:
Or...just build a 340 or 360. Considering mine is pretty mild and it made 470/455 and still has 13" Hg vacuum at idle with 9.7:1, I'd say they work. I'd have a whole 10ci on a 4" stroke 273 and easily 140 more HP. Head flow matters. Without going 4 valve heads, the small bore will kill airflow.