Those times are absolutely believable. In 1973 thru 1975 I had a 69 Z28 with the LT1 engine out of my 70.5 Z28. I had the optional off road '140' cam, an Edelbrock Tarantula intake and a 750 Holley double pumper. Remainder of the engine was factory stock. Ran a 4.88 gear behind an M22 and the car ran consistent 12.0's with an occasional dip into the high 11's. Had a lot of fun on the street with it too! The guy who wound up with it put in a 5.38 gear and got down in the 11.80's

He blew the motor buzzin it to 8 grand all the time with that gear - imagine that