i have to agree with chad here.
i have a '66 coupe as well and i can't stand having 4 drums, so i will be converting the entire set up to discs soon.
as far as searing boneyards for parts, you would need to pick up the parts interchange manual to see which cars you can scavange parts from with the lowest degree of difficulty. it's also going to mean that you may find parts that you would have to replace anyway. i think your best bet is to get a kit from one of the MANY mustang shops around.
if you haven't already done so, visit
www.cal-mustang.com and get yourself a catalog. the paddock (in san bernardino) is another great local parts source, as is larry's mustang in fullerton.
oh, welcome to the board! :s5 join a mustang club and you'll REALLY meet some people who can help you out.