Ouch. If you drive the poor beast at 60, with a 25 inch tall tire, (per previous posts), and assuming a final 1:1 transmision ratio, , your clicking around 3600 RPM's...far from the "...happiest..." RPM given by dave of 2100. The only way to improve milage with this set up is leave it parked! No amount of tuning tips and changed driving habits is going to help this scenario.
To keep the same tires, transmission, and lope around at 60 in the optimum range you need a ring and pinion ratio of 2.4. Good luck no matter what year.
Me, I would fall back on a new set of tall tire first, a 30" tall tire would get you down to about 3000 rpm @ 60.
Next I'd look for the 3.0 range for a R&P to drop you to about 2200 RPM. It is my guess that high a ratio in a 10 bolt is going to be hard to come by, if not impossible.
Look at the cacultor (
http://www.randysringandpinion.com by run) really close and pick your poison.
Good luck
Cavebull
