Lol, isn't this an alloy sandwich plate Corona box. A supra W55 has a steel sandwich plate for the input bearing and can handle 300 + HP, this thing is gonna pop if they put it behind a decent engine. I should start putting em On ebay, you can get em for $200 at the wreckers, make heaps of cash.
All W5x's pre 1988ish had alloy plates.
All W5x's post 1998ish had steel plates.
Whether the steel plate is much stronger than the alloy plate is a topic of debate.
If it is stronger, its only very slightly stronger.