3rz turbo would be legal in a ke70 under the new rules, should happen more often imo.
As for the hilux diff, you use the whole thing, not just the centre. A really early rn20 diff is similar length to a ke70, but are very hard to track down, and are also known to have weaker axles than the later versions. If $$$ is not a big issuer probably better off shortening a later model one really, the later one is also more likely to come with the gearing you would need.