Swapping a five-speed gearbox into an older car or ute is a pretty well-trodden path, partly because it makes all sorts of sense. While older four-speed gearboxes generally have a fourth gear ratio of 1:1, a five-speed is will have an overdriven fifth gear which makes for more relaxed highway-speed driving and, potentially, a fuel saving as the engine won’t be working as hard or turning as fast. The Toyota 2Y engine is, I believe, a more or less bolt-up fitment to the 2Y engine in your vehicle. Commonly found in early, rear-drive Celicas, the W50 is definitely strong enough for your application since the 2Y engine in your car probably struggles to make its full 58kW these days. The only catch you might run into is that if you’re running bigger wheels and tyres or your regularly tow a trailer or the vehicle is way down on power, the engine might struggle to pull that taller gearing. At best you might find yourself shifting back and forth pretty regularly in hilly country or when encountering a headwind. But if you do go through with the swap, you’ll find that the W50 has a fifth gear ratio of 0.853:1 which should reduce your engine speed for the same road speed by about 15 per cent. Beyond the Toyota E50 gearbox, there’s really no limit to what you can fit if you have the time and money to have the engineering sorted out. That said, anything beefier than the W50 is almost certainly overkill.