273 or NOT 273?

NC Engine Builder said
Not a bad recipe, but I'd either do a magnum head, or a 340/360 casting. The 318 casting lacks enough port cross section imo. And nothing is truly exotic about it, but if I were doing it, I would have a custom piston made for it, chevy pin diameter, and a metric ring package. The ring package alone is reason enough to go custom. With that, you can turn your 273 crankshaft rod journal to the generic "chevy" size, and have a much better selection of shelf rods, in numerous lengths. Allows you to shorten up the excessively tall compression height of the factory type pistons

this is answer right here.

in a game of "ounces add up to pounds" you want to take every advantage you can. a modern ring pack can be worth as much as 10hp and that number only gets better with a smaller, lighter piston with the advantage of better compression height.

if i was headed this direction i'd know two things off the bat: 1, it's going to be more $ per hp than anything else small block; and B the only things "273" left would likely be the block and the crank.