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