The serpentine belt. Engine has the 2ZZ tensioner (Some swap in the shorter 1ZZ tensioner.), 1ZZ air-con pump, 1ZZ idler pully, and a 2ZZ alternator. I tried measuring it with a piece of string. That doesn't work. Ends up way too short as the string sits down in the grooves. Looked it up on the net and got silly answers. The US 2ZZs might be different, who knows.
Took the too long original 2ZZ belt, cut it, wrapped it round where it had to go and marked it. 1675mm with tensioner compressed, 1715mm otherwise. Lucky for me the shop didn't have a 1675; nearest was 1700mm. I tried it. With the tensioner fully compressed I only just got it on. So after only two trial fittings, win.
Followed by an oil cooler saga.
The Corolla 2ZZ has one, a water cooled sandwich between block and oil filter. The JDM Celica 2ZZ didn't have one. My two dead 1ZZ motors, one did and one didn't.
I thought I'd fit the 1ZZ one to the Celica motor, but thread sizes were different. I started thinking they'd changed them at some point, but after dismantling the Corolla one, and looking up orifices with a torch and mirror, I realised there an extra threaded sleeve piece needed. Once that was in, no probs.