I did a little math, and it appears to be possible to use the 292 piston and rod in a 261, but not the 235. Offset-grind the crank to the 292 stroke, and you'll have a 292 cubic inch engine that looks like a 235/261. It gets the 261 cylinder wall a little thin, but it appears it wouldn't hit water. Boring the 235 to 261 diameter definitely isn't doable.
Jerry

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