Is that math right Mick?
Google thinks that the 250 has a 3.53" stroke and the 292 has a 4.125" stroke, for a difference of 0.595".
If my high school math is right that comes out to an extra 42.09 cubic inches. So I would say your right. For .595 I think Ill stick with the 292 block. I have a Mexican 292 block some say they are better some say they suck?