340 heads

Well to me it´s not likely there are two different X-head castings, we surly should have heard about that. Not that I have heard everything about SB Heads, but still... Since the 1.78/1.50” valves was a 273/318 thing, maybe Chrysler took what was available when they ran out of heads, and simply machined some 894 X-castings (´68 340 ) to fit the smaller valves, till new castings were ready to use.
I hope someone can straighten this out with casting #:s. Till than I somewhat provocative claim this is what happened...