To complicate matters, 3/4 and 1 ton trucks do not seem to have made the change to EEC. Possibly because whatever laws that GM were abiding by for the half tons they were able to sidestep for those "heavy duty" vehicles: I don't think that evaporative cannisters were standard on them.
http://67-72chevytrucks.com/vboard/s...d.php?t=645283