My Z10 has a zz4 crate motor in it with the original on a stand in the garage. I mention this so all of don't think I'm nuts for trying to find out what the top end is on the car. I've also installaled a speedometer spliter at the transmission which cut's in half my speedometer reading.
I live in West Texas where the roads are great and straight for miles and miles, so it's not really to difficult to find a place to make a late night run. My buddy also has a 69 with a highly modified zz4 engine which he drag races occasiounally. So, what do two 50 year old boys do on a Saturday night? We head out of town and find our top speed at WOT.
Since the speedometer in my car is reading half of the true speed, I found the rear does start to squat around 80 and the nose, with a front airdam starts to left about 130. At an indicated 70mph (140 actual) I got spooked and shut it down. The car gets really light in the front end. The car has a 331 gear in the rear and I'm sure I had another 10mph left it.
Ya'll come join us in West Texas.