Nice looking truck. Look under where it is parked a few drops of oil on pavement is fine, large puddles you'll want to check further. (Oil leak at rear main seal can kill a clutch) look at inside of wheels from underneath oil steaking on inside of tires/wheels can indicate inner wheel seals leaking or brake fluid leak. Check brake pedal feel if you have to pump it several times to get firm pedal you may have leak or air pockets to be bled. Does the charging system seem to be working? Lights? tires are they badly dry rotted etc. Most of these things are the same things you would look for on any truck regardless of age. Do a seargh on this page there was a DOT inspection thread you may find interesting. Final summary. If properly maintained it is perfectly safe to use and indeed would also make a fine advertising gimmick. Your road speed would proably not be much better than 55 with the 20 inch tires. Some trucks came equiped with 45 mph governors but I haven't run across one.
Good luck
