I am keeping my T5 and rebuilding it, I want to keep it for the antique value the car will have in my lifetime. The Z32 Transmission will not bolt directly up to the L28 engine but does bolt up with an adapter plate, see this link: Adapter
Yes they are heavier, but the T5 doesn't hold up to much power, I believe its around 300hp when it breaks. I am wanting to do a nice turbo build that will put me over the 300hp mark, so I don't want to have to deal with it then when it's broke now why not go ahead and build it like I want to, and not have to do it again.
On that note, I went to the junkyard and found a nice Z32 there with the manual transmission sitting in the backseat for me, someone had pulled the motor left the trans. payed $68, with that kit I will pay a total of $468 for a nice Transmission swap that will hold whatever I decide to do. My friend is selling me an R200 LSD rear end, so that will go in when I swap the transmission.