Starting with AMT kit# 38160 1971 Ford Mustang, I marked off the areas to be cut.
I used sheet styrene to make the trunk lid area.
I found the convertible top boot in AMT kit# 31859 1969 Corvair. (This kit is a hardtop, so imagine finding the boot there!)
A little sanding, filling, and primer...
I used Magnum 500 wheels from AMT kit# 31873 66 Olds 442 W30, and tires from AMT kit# 31937 1969 Mustang Mach 1