On both my JCB's, the transformers are located under the
pickup, screwed into that strip of wood with only one screw.
I don't know how to do pictures, and it would be hard to photograph without removing the pickup. Sorry.
The transformer has tabs with screw holes on either side,
on mine, it is screwed near the lower edge.( Look for the old hole.) angled down at a 45 degrees, off towards the lower rear of the bass. It kind of hangs off that strip of wood it is screwed into.
I hope this is helpful, I love my JCB's and have done lots of gigs with them. They are great! Hope your experience is positive.