Andrewv

I cannot believe that I remembered my password after nearly 4 years.

Over the years I have probably seen inside 40 or 50 evo/gsr gearboxes. I have only seen broken boxes from extreme use. The drag strip is by far the biggest culprit. Side step the clutch at peek power on a gripy surface in a 4wd and something must eventually give.
Keep in mind that these boxes will all eventually suffer from fatigue as they are not getting any younger.
Martins buggy has so much torque that the centre /diff Viscous unit could work out what to do with the drive. It often sent power to the wrong end. The Quafe was the only option and it works really well.
His box will brake at some stage and then I suspect it will get a full straight cut dog drive kit from Drenth. I have seen a few broken PPG and Albins boxes.
Any high HP evo/GSR with a std box has a marginal box for track or Drag work. My final words to anyone in any car with a marginal gearbox has always been "Treat it with a mediocum of consideration" (not sure if mediocum is actually a word). That means dont race syncros, allow the box to change gear, think about the mechanical loads and shock off the line.
As an example I ran a Toyota in the Vic rally championships for 10 + years with a T50 gearbox rated to 165 hp. I had closer to 200hp I never broke a box. Engine had enough power for me not to have to abuse the box. The guy I sold the car could not keep boxes in it. He over drove the box.
If 3rd and 4th are appearing to be a problem then this conversion looks the goods. Keep in mind that this may just shift the problem somewhere else.