Congratulations on your new aquisition.
As for the fuel question, doing a search will yield mixed opinions. My advive is to drive it the way it is and if it needs a teardown at some point, talk it over with your machinist.
Your truck will probably cruise at less than 50 mph. I would think that 45 mph would be cranking it pretty good. There are many on this site that can tell you from experience.
