You might try putting the pickups as high as they will go, just to have as much signal
to help you find the right balance (you can always lower them later, if you prefer that soundwise).
Also put the Q switch in the off position (normally, it's up) and have the filter and volume pots fully open.
Panning fully to one pickup or the other, you should be able to adjust the trimpots to set both pickups to about the same output level. Compare only the extreme positions of the pan.
If you put the pan dead in the middle, there will be a certain drop in volume - if it's a big drop then there may be an issue.