Brian (197064 buickspecial) had a rear panel a while back, not sure if he still has it. I found these, but couldn't find the complete panel he had. https://www.ebay.com/itm/64-1964-Bu...293450?hash=item2f2fac720a:g:NxQAAOSwE~1b2QXD You might pm him here on the board.
'64 tail light panel is one year only. '65 is similar, but has cut outs for series of tail lamp housings. (At least on Skylarks, not sure on Specials) Quarters, doors, hood and trunk lid, rear bumper, interchange on those 2 years. Front fenders, bumper, and grill do not interchange.