One other consideration- - - -with an appropriate amount of metal butchery by a well-qualified machinist, the lowly 235 can become a 270 cubic inch torque monster, using pretty well available off the shelf parts. Those parts just don't all bear the GM logo. It's not a simple, (or cheap) project, but there are many more 235's available to whittle on than the relatively scarce and pricey 261s.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!