How would that cause it to seize though?
Only by the piston getting jammed in the bore due to bearing slop. And those and not conrod bearings right, they are crank bearings?
So ya….
First ever 1FZ I tore down was seized but it was conrod bearings that went and caused the piston to seize in...
Start with the obvious, compression test and leak down test. Separate engine from trans if needed to perform the tests.
If you have not touched this yet, it came in and ran, then seized? Sounds like that is the case. Make sure flex plate isn’t busted, proceed to dropping the pan.
Obviously...