some late month 1966 chevrolet trucks had the 250 installed....it was an option as well as the oil bath air filter in 1966 and then in 1967 the 250 was installed in many chevrolets such as trucks and novas etc....whats funny is that all the websites say 67 was the first year of the 250 but my father purchased a 1966 chevrolet step side custom cab with that option from the factory in 1966 and the truck was ordered in january of 1966........the truck looks today like it did off the showroom floor.......with complete paperwork from canceled bank checks to window sticker.......truck still has the original chalk marks on the firewall......wink wink