For a car of that weight (about 360kg without engine for thoes more metrically inclined), the 1G should be a good size engine.
Most people hear are happy with a simple bleed mod to give about 150kw. I am sure that there is more in the engine with some head and cam work and If it is anything like any of the other factory turbo engines from Toyota, the bottom end will be plenty tough. I think the some of the valve gear (springs??) might be the same as the 4AG engines, so that might be a good place to start lookng. The 4AG's are a similar vintage design, so you may find that some of the internal parts are interchangeable.
Let us know how it all goes for you, I know there will be a few people here with more than a casual interest in these mods.
Good to see someone trying something different to the mainstream.