I'm betting you've already seen and considered it, but what about stuff from Super Six Motorsports? They seem to carry some mods that I've never seen anyone talk about. Ported intake manifold, ported heads, Cams, Stroker Crankshaft... A stroker crankshaft does sound like a pain in the ass to install, but going from 3.413 stroke to 3.60 stroke seems like it would make a good bit of difference, while still using pump gas, right?