help me understand my buick engine

just bought a possible 1950 263cui came out of a 1950 buick sedanet the visual looks like a 1948-50 engine from the book i have along with the location of the serial number boss but the first number is suppose to indicate what series of car it was in ? my book does not have a 60 series listed hoping someone can help me identify my serial number which is 61947324. hope someone can help me

 

http://www.buicks.net/shop/reference/engine_ident_52.html