Chevy 366 mpg modifications?

Ok guys this may be a little different then what yall are use to. I bought a 93 GMC topkick for $500, that came with a Chevy 366 bb. I'm wanting to use it as a work truck but its a dog and needs a rebuild. After the rebuild What are some performance mods I can do that dont require more fuel I can to free up more hp for fuel mileage? I know I can help it breath better with some long tube headers, a high rise intake, port the heads, and light rocker arms, and some spark mods and some modern 12 hole injectors to atomize fuel better. Any other ideas or tips? Its tbi injected and has a Alison 545 behind it.

Wow, Denny must be board......

Those 366s always seem to be struggling. Too bad you can't find a 427 tall deck to start with.

I also plan on running 4" magnaflow racing cats and flowmaster 40s with a h-pipe between them and run it out of stacks, because I can lol. But that should free up a lil more hp and sound cool