IGN had an article on it...
Yenko article
It isnt so much WHAT he did to them, as how many of them he did it too. To qoute the article......
"Yenko actually began sprucing up iron block Camaros in 1967, and added a run of Yenko Novas in ?69. But it?s like the man says, "the light that burns twice as bright burns half as long." Yenko Camaros disappeared after ?69 like druids in the mists of Avalon. Come across a genuine. Come across a genuine Yenko today and you might as well have found the Holy Grail or a batch of early Microsoft Stock. In any event, you?re set for life."
As for what they came with...
"Make no mistake; the Yenko Camaro was fast. This was back in the Good Times, when gas was cheap and passenger cars ran on something close to airplane level octane ratings. With 11:1 compression, an aluminum intake, forged crank and Holley 780-cfm four-barrel carburetor, the L-72 pounded out 450 horsepower and 460 lb/ft of torque at the flywheel. All this power spun into a 4-speed Muncie or TH400 automatic and hit the ground through a GM corporate 12-bolt rear with a steep-geared 4:10 positraction punkin. The aluminum block and intake sheared a couple hundred pounds of the Camaro's curb weight, which, combined with the motor?s raw power and better breathing through the ZL2 hood scoop, helped the Yenko Camaro trip the lights in 11.94 seconds at better than 114 mph in the quarter. The stiff F41 heavy-duty suspension included 4-piston disc breaks and a 1? sway bar, just enough to keep the handling respectable."