The first step is to throw out all the pots that they supplied you & buy:
two 500K Ohm linear taper volume pots (optional push/pull design for parallel/series switching of each pickup)
500K Ohm audio taper treble cut (tones) pot
If you're intent on using what was supplied, make your choice of blend or two volumes.
Personally, I'd rather have two volumes than a blend pot, for multiple reasons.
A. A blend pot loads the circuit more & reduces some highs & output
B. If that's a A/C taper blend pot, it reduces output even more by having a series resistance between the pickup outputs & the volume pot (even when the pot is in it's center detent)
C - ok, just two good reasons
Don't solder the capacitor between the treble cut & volume pot, like in that diagram. That's just bad practice. The cap should be contained to the treble cut pot & a wire run to the volume pot.
Those 250K Ohm pots are fine if you don't like some extra brightness & output.