In the not too distant future, I will be looking at a power increase on my Escort but the box I have won't last I dont think (well I know )

The new box will need to take around 350bhp and around 400 ft/lb of torque.

I dont really want to fit a mk5 rs2000 box as this involves cutting the chassis, but have heard that it might be possible to fit rs2000 internals into a s1/s1 box chassis

Is there any other options I have?