I checked a few months ago and it said.. 1239. The part numbers you seek have either changed to a new part number or no longer available from GM.  So I called them up to find it discont.   :icon_sad:

Inline 4s and 6 can get away with not having flex bellows because the head expands together with the pipes. Even so, they'll get some cracks. Even the Cast iron units get cracks because of heat expansion.

On V engines like ours, the heads expand at different directions and the block doesn't expand as fast/as much as the heads do. The pipes expand at another rate and size too. SO those flex bellows are needed. Even having one flex bellow is enough.