Will box blonde dye take the pillarbox red out of my hair? Atleast to a shade where I can put Napalm Orange over it and it be bright?

Never tried that. Venturing into something with a color I have not tried. Though I had success with a bleach kit and manic panic green. Good luck.

I've heard mixed results from trying this. Some people swear by using a box dye to remove colour and for others it does nothing (I'm the latter).

Sorry I can't be more helpful but would be interested to hear how it goes.

Maybe if it was a high lift blonde it could work, but normal blonde dye did nothing when I tried using it once on someone's faded blue.
If you're worried about damage you could always do a series of bleach baths instead.

If you use a high lift or ultra light blonde dye, it should work. I've used Garnier 100% Colour in Extreme Biege Blonde to strip Punky Colour Blue Black out, and I've used L'Oreal Excellence Blonde Supreme Cream in Extra Light Ash Blonde to strip out a mix of SFX Atomic Pink and Cherry Bomb, both times with excellent results. If you do want to use box dye to strip out colour, I'd reccomend the Excellence Cream. It comes with a pre-colour serum that really helped keep the dye from frying my ends.

But I should warn you that if you have significant roots and your hair is darker than maybe a dark blonde, you'll end up with bright gold roots, no matter how long you leave it on.