re: Retractor Covers
Nice job by the way!! I am completing something similar to yours and know the challenges you've faced.
As for the retractor covers, they simply "sit" over the retractors and on the floor up against the rocker panel. Once the carpet is in, the seatbelt guides (black plastic with slots in them) attach to the retractor covers with 2 screws.
Hope that helps.
ps: What motor have you got? 383?