Well it would move it up a gear, maybe, but you might be more in the power band?
Anyway, that's the important thing - get the gears closer so you've got a bit more freedom in gear choice, and it won't hurt your time as much when you stay in the higher gear round that corner.
Part number here, seems they come as a set... I've no idea about compatibility, but I can't see any obvious reason why not. As far as I can tell from the EPC, the same gears are used on the open and torsen diffs. I have heard of a similar swap being done to Soarer diff (it might even have been a Supra NA diff being fitted to a Soarer, since they're compatible). So... hopeful, but I can't confirm it.