I'm pretty sure they still make the 3550, infact, I'm almost positive, as I think ecu 5.0 from this site is ordering one...ecu..you out there???
don't waste your time with the t5z, it blows. just another t5 trying to be a real tranny. It's not gonna hold up to abuse for long, powershifting, 5k throttle drops, etc. sure if you're nice to it it will hold up...but why??
get yourself a brand new tremec for around $1300. try d&d, that's where my bro got his, and they were super cool. You'll need the tremec bell for another couple of hundred. If you can find an early srod bell, that will work too and save you cash.
my bad, he's getting the tko I checked d&d, and saw no 3550s. very strange, maybe they did stop production. they did have alum shafts for only $174 though.