Take that website with a BIG grain of salt- - - - -lots of incorrect information, and more than a little bit of info from "other sources" without attribution.

The 848 head needs some modification to work properly with a 261 engine- - - -some of the cooling passages don't match up to holes in the block. It's a fairly simple matter of drilling a few small holes at the right position and angle, using a 261 head gasket as a template.
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!