Yes. Since the 340 was already in production, they were just coming out with the 360. So any updates to the heads were charged off to the 360 program as it was a "new" engine and they can write off tooling costs for new products for a tax break. Any tooling costs to "maintain" existing tooling for current production is not able to get tax write offs. So they made the changes to the heads that would fit both engines and charged it off to the 360 program. Then could make the new tools early and "pull ahead" the change a few months before the 360 was launched and put them on the 340's. They then put the cast in 360 on them as the new changes were paid for on the new 360 program.
The tax write offs give incentive to the auto companies to keep coming out with new products instead of maintaining the "same old, same old"...