A 98 Ra box won't be 4.11, All JDM WRX stuff after 97 is 4.44 even the povo models.
If you're lucky it may just need a mainshaft. If it needs a mainshaft and a second gear (usually a third gear synchro as well) it gets to the point of not worth it on a stock 99/00 3.9 box.
Personally I wouldn't de-value a 99/00 with an earlier box than what the car came with (although 4 bolt boxes will fit) I'd be searching for a nice late model 4.44 box without close ratios. (unless it's for racing use primarily, then close boxes are the go)
Any box that's been apart and 'inspected' by someone other than a reputable workshop should be treated with suspicion.
In answer to the original question though, I have various 4.11 diffs available.
I have some New, old stock genuine 3/4th sets but no second gears to suit yours.