Congrats on the find and on the finish!
One hint for next one and to get those stains out that you mentioned is to degrease the skull before whitening. The initial whitening process makes them look nice, but after a while you will probably notice yellow stains creeping back through. If you don't care about a perfectly white skull then you can skip degreasing, but for longevity of the whiteness degreasing is a must. I soak mine in 120 degree solution of water and dawn dish soap, changing water every other day or so. Usually it takes a month of doing this to remove most of the grease. I have had one soaking for 3 months (really old and stained) and still am going at it. Acetone bath will help too, just be careful. Dont heat the acetone.
Congrats again!