suped up 6

Think of the engine as a giant air pump. The more air you can move through the pump, the more power it produces. Headers & 4-bbl carb are two ways to help it. Other things are cylinder head porting and increased valve opening through camshaft changes and/or larger valves.

You didn't say which transmission you were working with. The 904G and the 833 are plenty stout. The all-synchro 3-spd manuals are fine. The ones without synchro on first would handle the 273 2-bbl ok, they just aren't as easy or fun to drive. Hope this helps.