Well I worked for Jim for 15 years, and Cotton's engine is the one I was referring to that made over 600 HP. It actually made 612 HP the last time it was dynoed just prior to Indy in 1986, when Cotton drove the F/Dragster of Brian Browell. Cotton actually set both ends of the record for that class at that time. Also, many publications are full of misinformation, either mistaken or intentional, so don't ever believe everything you read in them. But, I can assure you, that there have been quite a few since then that have also seen HP levels above 600 as well. The only thing that was changed on the engine the way it was run in Cotton's Chevy II, before it was put into Browell's dragster was the headers and the oil pan, nothing else....I've also seen the references that were used in Leo's book that were quotes where he was asking Jim about certain subjects like camshaft info and head flow. And what Jim told Leo, was very conservative, in reality to what was actually being done at that time. Jim was extremely secretive about any pertinent info regarding his techniques or knowledge about his engines, and would have never divulged any kind of info that wasn't already public knowledge. Not that Jim intentionally mislead Leo, he just told him things that were done 10 years earlier, and not current methods or concepts for that time period....
