there are warehouses full of brand new mustang parts for sale, mustangs are very popular, the best thing to do is like the other answerer suggested, go to school and learn how to fix cars from one end to the other. In the process you will learn about all the things you need to know. There are warehouses dedicated to preserving these mustangs one company " yearone.com :" has lots of information and catalogs you can order . Another big one is " classic industries.com" this is another online warehouse but I know there are plenty more. I always liked how roush mustangs looked, they have body kits, interior kits, and you can buy a roushperformance.com motor that will blow the doors off anything. Ford had a 289 small block that you could turn into a 600 hp motor. and there are many others like the Boss 302 and the newer mustangs have these 4.6 v8 that are some big horsepower motors in a small package. I always like the late 60s 351 windsor and both ": ford performance.com " who has a 351 boss new last year that your dad would probably love, and " roushperformance.com:" have motors built along the 351 that were and are still popular. In the end, you spend a lot of time looking and reading and doing research, and save your money and make that mustang your own. And please try to pump your dad for information, you said he knows a lot? good, he is your absolute best source to ask when making purchasing decisions. I love those old mustangs and that 66 is going to be worth a baby fortune with a big block in it.
I have only mentioned a tiny bit of the information available for your mustang. you can type 66 mustang? in the web search box too, and a lot of stuff will come up that way as well.