56 Packard tail lights are cool and were popular on customs since the 60s. See the picture below. They're hard to find though and expensive. $400 or $500 each for a complete unit on ebay when they show up. The back end of the fenders were welded on and leaded. They used the 54 quarter panels underneath. They were shaped more like your Buick before they added the cap. Another good one is the 56 Caddy. You'd have to cut off part of the Caddy quarters and mold them in.