I've made several long runs, first in my '85 (1.9l) and now my '90
(2.1l) with no problems due to length of run.  Example: Shasta to
Lynnwood (north of Seattle), about 650 miles, with only stops for gas
and food, maybe a couple of long stops (30 min) at rest stops.  If you
cooling system is working okay and everything else is up to spec your
only problems will be a sore leg (if no cruise control) and a good case
of TB (Tired Butt).