so i am getting ready to do the shelby drop on my 67 but my longtube headers are already slightly rubbing on speed humps if i go to fast (not real fast at all thought) so if i do the drop and use the 1 inch spring insulators would that just negate the drop or no cause i want the better handling but i don't wanna destroy my exhaust

 

I have the S/D andlong tube hedders. I got tired of smacking speedbumps so put a size taller tire on the front and back, that did the trick.

The pic of my car is before I put on the taller tires. You can see how low she's sitting.

 

You lose about a 1/4" from lowering the upper control arms 1".
If you were to use a 1" insulator you would gain about 3/4" of ride clearance assuming the same coil spring was used.