[joe_padavano]

You can do this with a Chevy because both the 350 and 400 are small blocks. The fact that the 400 crank will drop into a 350 block allows the Chevy types to build a low cost 383. There's nothing magic about this displacement, it just happens to be what you get when you combine these existing factory parts.

Now, as others have mentioned, the Olds 400 is a big block, the Olds 350 is a small block. These are completely different than the Chevy motors, so Chevy ways of building things don't apply. Now, the major external difference between the BBO and the SBO is the taller deck height on the BBO to allow for the longer stroke. There is also a key internal difference, in that the BBO uses larger bearings than the SBO. The bore spacing is the same, so theoretically you could have a BBO crank turned down to fit an SBO block. The easy alternative is to use an Olds diesel block, which already had BBO-sized bearings. Of course, then you get into things like custom rods and pistons, which rapidly escalates the price.

The better question is, why bother? The 403 Olds is a small block and is a direct bolt-in for the 350. Note that all SBO cranks use the same stroke, so it's worthless to swap a 403 crank into a 350, you still get a 350 (however, swapping a 330 crank into a later 350 or 403 gives you a forged crank). And while the 403 is a direct bolt-in, it takes very little additional work to also swap in a 455 in place of that 350. Either the 403 or the 455 (or 425 or 400) swap will be less expensive than the custom parts needed to build a 350 Olds stroker.