So GM comes along with the idea of taking the displacement of the good ol' 5.7L out farther, digging into the aftermarket 383 market...but their production-line equipment isn't set up for 4.030 boring/honing. So getting an engine that can be marketed with the 383 recognition means using the standard 4" bore so the block can go down the normal machining line without tooling changes. Then they add a couple of cubes with a touch longer stroke. Given the GM buys heaps of them, it doesn't cost them any more to specify a 3.80 stroke instead of 3.75.
Price a GM 3.8" stroke crank. The aftermarket kills 'em with the more-common 3.75 stroke Chinese stuff.
Ah, so that's reason the GM "383" uses a slightly over-stroked 400cid crank... so they can continue to bore at 4". It's so obvious, I missed it.
So in my remarks earlier, i.e., "refurbish an L31", it makes sense to do the typical thing with .030 cut on the bores and a more common 3.75" stroke crank to get the 383cid.
It's worth mention that the 3.8" stroke crank in a .030-over block yields 388cid.