The block no 3970010 was used for more than ten years. In both 2 and 4 bolt main. Cast in Saginaw, Michigan. The heads 041 were only used 69-70, on the 300 hp. 4-bbl 350. The heads are almost direct copies of the "Camel backs" with acc. bolt holes in the end. Stock, they were 1.94-1.50". Flat top pistons were OEM and cranks were iron.