i duno exactly for na to turbo rear breaks but i could check cause i do have both sitting in my driveway, but i know that almost all cars with disc's at the rear run drum breaks for the handbreak, i cant see y they would change the set-up or even how they could change the set-up for na to turbo, so im quite sure that they would have an inner handbreak and outer disc's for the breaks. i think that the workshop you called probperly just couldnt be bothered, because i know silvias use na 33 brakes as un upgrade then turbo brakes for 5 stud set-ups, i think the main difference is the disc size i dont think you can put na calipers over turbo discs because they are too fat but and like wise the na's are too thin for turbo calipers but if you are transfering everything it should be ok just make sure you get a brake booster too otherwise you'll have less pedal and more sloppy feel.
if your not willing to go with the swap just upgrade your pads and disc's at ther rear that should be enough of an upgrade to take a tubo conversion or more power ect.
ps HAME leagly you will have to have at least the equvelent of turbo brakes for it to be leagal and roadworthy, if you get pulled over they might dick you!