RE: Radiator overflow tank and fluid
eep4life, I had one of those plastic kits once. Worked ok & easy to install. Just looked a bit ugly. Usually need to drill one or two holes in theinner fenderfor the screw mount. Then route tubing to it from the orig overflow port thats under the cap. Never gave any thought to what cap to use. Been using the standard replacement type with a lifting lever on it. Your stock rad holds 13.5 quarts, 15 if its AC equiped (according to my shop manual).
Mustangs plus sells a Stainless steel overflow reservoir for $67 if you are into dressing it up. Tube shaped and can mount along side your radiator in the stock bolt holes. i like the cleaner look.