if you want better mileage, then higher rear gears are what you want. the power to fuel mileage differance in the 170-200 is minimal.
i have 1 pickup with a 144 and 1 pickup with a 200. both have plenty of power, and both get better that 20 m p g on the highway.
the truck with the 200 has 3.50 gears, and the truck with the 144 has 4.00 gears.
little motor cruises at 55 real nice. 200 cruises at 65/70 real nice.
actualy that order didn't come through, so I had to rebuild the old 200
but I know somebody who eventualy will sell his 200 plus manual trans and exhaust
with about 10k miles for $500 when he is ready to do a swap with a v8
I just couldn't wait for it
try those guys http://www.wla-engine.com/default.htm