Casting number 3956618 was used for the following engine blocks: 1969 - 302 used in the Z28, 1969 – 327 used in full size, and 1969 – 350 cars and trucks.

V = Flint
04 = April
25 = 25th day
WI was used for 1967 – 283 used in 4 wheel drive trucks (K-10 to K-25), 1968 – 307 used in 4 wheel drive trucks (K-10 to K-25), and 1969 – 350 GMC ¾ and 1 ton pickups with 4 bolt mains.

My guess is that you have a 350 from a GMC pickup

Regards,
Glenn