The Reo truck shown is based on a 1929 Reo Flying Cloud. It should have the Reo six 3 3/8 X 5". The Serial number should be on the left frame rail next to the steering gear. There probably is a sheet metal shield over it. I could not find any factory photos of Flying Cloud pickups. I did find the attached photo of a 1930 Model 15 also called a Speed Wagon Jr. It had a Continental six, 3 3/8 X 4" with a standard 115" wheelbase. The R. E. Olds Museum has a ambulance/hearse with this chassis. So, can't prove the truck was factory built but could with the S.N. Reo would build anything that they could sell during this period. Dave.