I'd start with your 273 block and bore it 0.030. Use the 4" crank, stock length rods and custom flattops. You're now at 335 cubic inches. Or the 3.58" crank right at 300 cubic inches. I'd use Magnum heads with a decent valve job and a Performer RPM. A 600-625 cfm carb would top it off. I'd suggest a single pattern cam with about 210 degrees duration and the biggest lift you can find ground on a 110 degree LSA. With headers you'd be above 300 hp and 350 lb-ft torque easily, it's pull so hard you would be amazed.

It's so much easier to make power with a slightly bigger engine and you won't have to run 4.56s to keep up on the street.

R.