'86 E350, 460ci, looking for suggestions

[pstrbrc]

I'm picking up an '86 E350 coach (dual rear wheels, 20 seats) that I'm planning on converting to an 8 seat + sleeping bunks and kitchenette race car tow vehicle. The 460/C6 got ~8mpg last time it was driven (about 7 years ago!) and I'd like to do better. Here's my thinking-
rebuild carb (isn't it a 600 cfm Holley 4160?)
find a good E4OD, use a Baumann controller and shift kit.
put in a "tow" cam, ~204*/214* @ .050, 112* cam lobe separation
Cam chain drive w/adjustable advance
headers and large turbo mufflers.

Outside of getting rid of the 460 for a diesel, are there any other things I can do for fuel economy? Would fitting a later fuel injection manifold and related stuff be worthwhile?