I drive a carb. Get 18+ MPG at 70 MPH. Carbs are outdate but they do work when properly adjusted and setup.
Without an engine transplant, aftermarket TBI/MPFI installs are available. Read this article:
http://users.sfo.com/~eagle/howell.html You'll get a good idea about using stock parts from a donor vehicle. You can even upgrade a few parts for better performance. You can buy parts from
http://www.cfm-tech.com/