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For that large a difference in basic bore, I'd guess they cast the 254's with different cores. The .060 limit on the 226 may just be the limit of O/S pistons supplied.
The heads are different, but will physically interchange because the bolt pattern and bore spacing is the same. That's not to say they should be swapped because the combustion chambers are definitely going to be significantly different. As I mentioned before, the blocks are the same physical size, externally, but are different castings with a larger bore and a different casting number, so internally they're going to be different.
If that is the question, either engine will fit in place of each other. They are identical, physically.
I have a 226 and have been looking for a replacement exhaust manifold. If these two blocks are physically identical does that mean that a manifold off a 254 will work?
Just trying to think - If the water jackets on the 226 are bigger that means better cooling than the 254 which should work harder (larger Trucks) and run hotter? - Do I have this bass akwards?