The 50-52 235's are unique. They have a different head than earlier and later 235's. Between spark plugs 1 and 2 is a large flat/ slightly curved area. Same between 5 and 6. It also has 15 bolt holes. All 53 and later 235 heads have 18 bolt holes and are interchangeable, with due consideration given to lifters, push rods and rocker arms... The 50-52 engines, and 53 non-Powerglide engines, are "low oil pressure engines" with babbited rods, dippers and oil nozzles to oil the rods - no oil pressure to rod journals.
