the GX460 and Prado share more than just the underlying frame/chassis and are pretty much the same vehicle except minor exterior bodywork, I would say 90% mirror of each.
where as the 4runner mostly just shares the underlying frame/chassis with the prado and pretty much nothing else. I would say about 10-20% mechanical wise.
just from experience and opinion. I imagine someone will probably chime in with better/exact stats.