The slanty can make power and still be a miser.
Check out the Slant Six Forum.
They do have a recipe that can give you power and economy.

http://www.slantsix.org/articles/articles.htm

Between 1978 and 1981,Ma used a 2bbl intake and carb,and 2-1/4" exhaust for more power and torque.Yet it still maintained good fuel economy.
A common swap is to install the Super six gear on an older slanty,recurve the dizzy,install a clutch fan and shroud.
Plus -as mentioned-go with 3.23's in the rear.
It will run forever and make more power than smogged up late model 318 in a 5Th or Dippy.