Try a Carter YF for a 258 cubic inch American Motors/Jeep inline six. It should be about as close a match, cubic inch-wise as you'll be able to find, and there's usually a few on Ebay at bargain prices. The 258 was actually an international truck engine that AMC used in the late 1960's and early 70's in several of their vehicles like the Rambler Classic, the Hornet, the Pacer, and a few others. It should also bolt onto the 261 intake without an adapter. Good engine!
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!