The 261 is, physically, much larger and MUCH heavier than the 250. The cylinder walls are thicker the stroke is longer. It's essentially a larger bore 235. Obviously it has 11 more cubic inches.
The 250 is physically smaller and lighter than the 261. But it has several advantages over the larger engine. A 7 main bearing design makes the bottom end more robust when balanced. This plus the shorter stroke allows the 250 to safely turn more rpms. And with the newer v8 style bellhousing the tranny possibilities are tremendous.
The 261 probably has more torque factory stock than the 250, but the 250 can be built cheaper for high performance than the 261, and probably outperform it. Another tremendous advantage for the 250 is that replacement parts are readily available at most any corner auto parts store.
If you can find one cheaply you might want to consider the 292. The 261 has absolutely no advantages over the 292 - none. Unless you consider larger and more weight an advantage!
Be good!
-ftyler
