Cut 17" off mine earlier this year - its a 4 door 86. For the rear wings I cut them vertically about 1" in front of the flange where they join the rear quarter panel that houses the rear lights. Then unbolted the flange and you are left with the corner to fasten the new wing to. Then cut the remainder off the rear of the front wing ie in my case 16" ie 1" on flange + 16" on wing = 17" I was shortening it by. You then need to ensure that the flange fits neatly inside the end of the shortened wing panel. Once you are happy use Tiger Seal - a body adhesive available from all good car panel factors , to join the 2 together - I used about 6 small strong clamps to hold them tightly together. The ones that operate like sealant guns are ideal. Leave overnight for the Tiger Seal to cure then repeat for other side.
Bolt back to rear corner section and bolt back on car! I used a domestic jig saw to do the cutting and a hand file to ensure a good fit.
