T-56 Mag or Tranzilla?

[D-$]

I had always planned on doing a T-56 mag and a SC LS3. However, that plan changed a bit when I found Mike Redpath from Musclerodz & Customz engine for sale.

https://lateral-g.net/forums/showthread.php4?t=50890

My question is what kind of tranny do I need to be look at now. I will be driving street 80% of the time, Autox, track the rest of the time. I have been told the T56 mag can handle up to 1,000hp but I don't want to be sorry I didn't upgrade from the start later. Would anyone have any thoughts on the matter?

Side note:
I plan on running the new speedtech subframe.

Thank you for your time

D-$