[68post]

...yes, I do know the bore and stroke (and of all 3). Have a '71 307 languishing in the garage right now, shame it's of no use to me - it's low mileage.

The very small bore of the 305 helped with emissions - which at the time was probably their main concern.

GM's small engines have a history of using existing current (at their build time) crank strokes of their larger brothers.
Olds '68 to '69 400 and 455.
Olds 260, 307, 330, 350, and 403 - all the same stroke.
Buick 430 and 455
Pontiac 326, 350, 389, & 400
Chevy 307 and 327. 305 and 350. 396 and 427