That math doesn't add up. The de facto 4 inch crank would require a .090" overbore on a 318 to get up to 402 (Hensley Performance does this on early blocks after sonic testing). A 406 is typically what one gets with a stock bore 360, and 408 is a 360 with .030" overbore. Don't guess he spilled the beans on his dimensions?
An easy build would be 318 with .040" over and a 4" crank. That'd make a 392.

