Remove your door panels and see if there are holes filled in. (rear quarters-Front fenders also are pierced) also check if the light buckets are R/S style, check if a vacuum canister was removed, Check the light switch,
Check if the rear panel under the bumper has been filled in. 68 R/S questions are rarely answered... We middle kids need to stick together. I am no expert but 30 plus years of 68 R/S cars has provided me with a little insight. Any help i can provide I will.