Jeff Nichols

""Get a copy of Performance Tuning the Sunbeam Tiger, it will answer a lot of questions you pose"

I wouldn’t trust that book. That is the source of the rumor: 260 block with three freeze plugs is the same as a 289 block but not bored out to 289 specs. Any info in it pertaining to 260 performance is 40 years out of date. Its an interesting artifact to read but don’t base performance mods or rebuilds on it.