Bill, The adjustment issue you're having is discussed in detail in the '57 Shop Manual - I presume it's also in the '58 book. Depending how much adjustment you need it may be accomplished with the attaching bolts located on the roof rails above the vent window. If more is required, you'll need to remove the rear upholstery and move the whole top frame forward. I would advise getting a manual and understanding what's needed. It can get involved because some of the adjustments can be interrelated to, and effect, others.HTH,Ralph
Folding top adjustments :section 17-65 to 73 in 1957 Cadillac Shop Manual
Bill,Page 15-19 of the 1959 shop manual covers adjustments to the "folding top".