That Shelby looks like an original issue because of the separate red taillights. Not big value difference, but the glass changed after the Modern Classics series. No idea why.
Cougar nice, all there mostly, can get chassis stuff, exhaust, firewall from 69 Cougar reissues that are pretty common. It has front and rear side marker lights it's a 68. You can see rear side marker in pic of the Comet rear end.
The frame and pickup bed floor probably from the Revell Willys pickup. A bit hard to tell, but seems that is it. Skippers Critter Anglia is the bodyless red car, original issue molded in metallic red.
Single axle trailer is from AMT 64 Vette I'd think. The Ford and CHevy trucks have the trailer that exists in some of the 3 car sets. Fireball 500 has a 2 axle trailer similar to that.