I had an 84 S-10 1.9L that got 33mpg @ 65 mph after I advanced the timing a little. I was looking for another one about 3 years ago, when I found my current 1999 Chevy Metro 3/5. Anyway, I think if you played with the timing a little as well as different octanes and hypermiled it, I don't see why you couldn't hit 40+ on the Ranger I4. Aren't they rated for 29 or something like that on the highway? You oughta beat that by a whole bunch!
If you find a Metro that has a wiped motor for cheap (and the rest of it is ok), invest some $$$ and get a $395 (+ shipping) JDM motor. That investment might pay for itself in no time...My JDM I bought from these guys has lasted close to 50k miles so far.
Nippon Motors