I am restoring a 66' Chevelle SS396 Coupe. The car was equipped with air shocks on rear when I bought it. My concern is if I go to gas shock absorbers will I still be able to maintain a level stance on car with out any noticeable sag in rear. Some cars from that era had a tendency to sit low in the back. Any suggestions or advice? (ie, stick with air shocks or a particular brand of gas shocks.......I have KYB gas shocks on the front). Thx Larr