Phil,
For short periods, but I'm sure like the rally teams you'll replace it regularly anyway .

If you want the PUNCH and aren't interest in top speed, go to the 3.9 diffs .

If you think that would make a nice road engine, you're living in a dream world. Listen to what I said about having been in the car thus equipped (I'm talking about an Ex-Ford works car as well - one that cost £250k to build ). My sapphire which only had 385bhp would have MURDERED it on anything other than a rally stage or really tight twisty track. I was so dissappointed with the performance it was unreal (obviously the handling was on a different planet, but on track, it's power and gearing would have hampered it beyond belief).