What can an O20 gearbox take?

I've just bought a G60 cabby with an 020 gearbox in it. I'm wanting to tune the G60 but how far can I go with this gearbox without breaking it or are they just as good as an 02A?

Good box, but you really need to fit a diff bolt kit to put anything over 130ps through it. The 02A has supposidly stronger internals but I've seen them with the same bearing & gears supplied as the 020.