I was a huge fan of Nirvana but was never interested in this guitar until I saw (and hear) it's the main axe of Ruban Nielson of Unknow Mortal Orchestra Huge sound and playing, very particular. Check out their live videos and last album Multi Love.
I did the same made mod than him : Lace Sensor Gold single coils.
Also did a Mustang mod for the 2 switching selector :
Left : Bypass (direct to output Jack)
Middle : Volume only
Right : Volume and tone (normal)
Complete new cloth wiring and new CTS 250K Pots.
Paper in oil cap.
Bridge locked, spring removed.
Tortoise Pickguard.