That is my understanding also. White Spirit (UK) = Mineral Turpentine (AUS). And yes, 50/50 (1:1) White Spirit/Polyurethane.So it seems that white spirit might be right thing for this?
Looking at Big D's video, a bit sanding in the middle followed another hit of yellow dye should get you where you want.
I have not done a stain burst other than mucking around on scrap, so can only go by what I've seen on YT.
Yours is looking really good though! It's a shame that body requires such a prominent pickguard. It would be nice to show off more of your hard work there!