I'd say go 331 with a good single turbo. I'd say 60-1 being the smallest but I wouldn't go bigger than a t-67 because you can make more power than your block will hold anyways with the t-67. Spool up will be good depending on set up. You have a v8 so low end will be there with the right turbo cam. You can do dual exhaust on a single set up.
twin turbo = cold side is a bitch, hot parts are easier
single turbo = hot side is a bitch and cold side is easier
There are kits for both, there really ISN'T any benefit going to TT than a good single, unless you do it junk yard style then TT would probably be better as there are tons of the right size turbos you need that are cost effective.
Just use your same s/n and password for turbomustangs.com . You will not find a better turbo mustang site than that.
There is not enough time to get into what a/r you need for hot/cold side of the turbos, but you will come to know from searching.