MPG The Best Of Both Worlds

I wouldn't go any bigger than a Comp XE268 or Lunati 60403 (pretty close to the same cam's). Main reason is the compression is too low to really support anything bigger than that. A smaller cam like either of those will make a lot more bottom end torque than what you have. That will work better with your combination as a whole IMO. With a smaller cam like one of those you could also go to a 3.55 or 3.23 gear which combined with the cam and swapping to a vac sec. carb should increase the fuel mileage markedly.