height isn't the issue....tho the stock springs will eventually sag if you have a winch/bumper on the rig...the rig I have now (with 71,000 miles on it) does sag in the front some...big surprise with the use we put them through.
the issue is in the shock stroke....with a stock suspension the shocks are at the middle of their 8" stroke....4" up and 4" down. Because Revtek spacers install between the top of the spring and the upper coil 'bucket', they move the springs down lower in the shock stroke, giving you 6" up and 2" down...since the coils bind before the shock compresses fully, your actual travel won't even be the full 8".
(I think it's 8", don't quote it, but the theory holds...might be 8", might be 7", might be 9", but either way the stock ride height is in the middle of the shock travel)