More work on the Plum Crazy GT

Leave the button auto (we're all getting older) and stick a 360 in it. You'll need a pricey convertor with the early stator and later hub but that's not a big deal. A stock ot similar 360 will exceed the 273 with bolt ons in terms of butt feel. Even with the factory 273 manifolds and single exhaust. That's what I'd do.