Slant 6 MPG Upgrades?

My experience with TBI vs port injection is that the jump in drivability and mileage between TBI and port injection is about the same size as the jump from a carb to TBI. While this may not be cost effective if the goal is to save money, if the goal is to optimize the slant six to see how far you can push it, I'd call up Gill Welding for a multiport manifold. As for an ECU - I'm kind of partial to the MegaSquirt III line, but if you want other options, the Holley Terminator designs would be a solid choice. I'd steer clear of designs that simplify things too much, the ones that advertise "no laptop" as if that is a good thing.