If 3.73 gears are best for an A4 and 4.10's for a manual tranny, then my question is will it be ok to run 4.10's on a full manual A4. You know one of those TH700R4 with a full manual valve body, not a shift kit.

 

Unless you're running one hell of a tire, I think you'd find 1st gear entirely useless with that combo.

Other than that, I can't see why not. I ran a car for a while with those gears and a Turbo 350.... but even with that, 1st gear was too short. Even with the gutless motor that was in that particular car, near as gutless as a TPI motor actually, I could still smoke the tires right off of the car and sit still, if I was the least bit careless. I don't know what you've got under the hood of course, but I think you'd be likely to get the same results or worse with the bigger inches.