Hi again @chris_b I would of responded properly much sooner but I was working away.
My reason to change...
I felt that the 'P' part of the originally fitted PJ sounded uneven on a string to string basis - yes, that should be easier to set the pick-up heights etc. but there was definitely an imbalance. I purchased a new P pick-up & removed the old one.
On removal, the original 'P' had a wire squashed between the winding & the cover ... which could explain the unbalance.
I fitted the new 'P' pick-up & the balance that was missing from the original pick-up was restored.
Unfortunately the balance between the new 'P' & the 'J' pick-up is uneven (Doh !)
So now I am thinking of fitting a 'matched' PJ set & was requiring info on what sets could be fitted to an active bass, hence the original post.
I hope that is clear?
Jason