I have a 1989 c1500 2wd standard cab shortbox. We want to jack it 6", however the closest thing we can find is a 4" and it only fits 1500 92-98 standard cab and 88-98 extended cab. Whats different from 88-91 in the standard cab that it wont fit? fabtec has one i think that will fit but it runs around 1500.00. and the ones that fit 92 are 500.00. is it the front, the rear, why wont it fit?