You should probably be more specific. There were 2 styles. One was an early 60s T-bird tail light, and the other came from a 67 Cougar. They both would require very different mods to install. Also, if you got the dough, there are modern LED versions of the T-bird light that are flush mount. Therefore other than drilling a couple tiny screw holes, there are no real mods. Might be worth the extra dough just for not having to do a bunch of sheet metal work on the tail panel. There are also different mounting options. Some folks mount the lights straight to modified Maverick tail panels. Then a couple folks, Razorsharp is the most obvious, have replaced the Maverick tail panel with actual Shelby tail panels. (Fiberglass that can be had as repop)
All I did was cut two big holes and drill small holes for the mounting screws. The housing attaches inside the trunk, bezel and lens outside. Get a cheap sequencer for the turn signals here: www.webelectricproducts.com
i just got my 67 cougar tailights i won on ebay. they dont look as good as i expected. and they are heavy as #*%& . i was going to buy the fiberglass panel and do the swap but now im not sure. i think im going to resell the lights and stick with the maverick. if i do it i'l spend the extra mony and get the panel with the sockets built right in. those cougar lights are HEAVY!
If you click the link in my signature that says restorations pics, you should get an idea of the way I did mine. It's time consuming but I think well worth the effort and expense.
After welding in flat sheetmetal to do mine, I think what Ray did was actually easier. It was a LOT of welding -- like doing a 3rd quarter panel! If I decide to I can always buy the fiberglass panel and bond it over what I've already done, since you have to cut out the raised part regardless of which way you go. One thing, the Cougar assemblies don't mount the same way, so you really have to buy the Shelby light setups to do what Ray or I did.