I see you're measuring with the rear curtain off. Did you measure the bow height of the old top before you took off the top and rear curtain? 20 1/2" is the correct bow height for your Chevelle, but if the old top fit correctly with the frame like it is now, leave the entire set-up alone. If the old pads are still good, just leave them alone also. Just make sure that the seam across the back of the top, if there is one, sits in the middle of the rear bow so it can be covered by the wire-on. In other words, don't change anything unless your new top doesn't fit with the old rear bow height.
Don't let the science of installing the top (the measurements) get in the way of the art of installing the top (adjusting the top to make it look good), and vice versa. Does that statement make any sense to you?
No one lives forever, the trick is creating something that will.
Last edited by DanTwoLakes; 08-04-2012 at 02:32 AM.