Hello Stef, I’ve only just seen your questions. A friend who lives nearby is about to rewire his Slough Big 6 as part of a complete restoration. If you ask specific questions about routing etc, I can go round, make notes and takes photos and forward them to you. There is no trim fitted yet so it should be clear to see and the 6 wiring must be very similar to the Lt 15.. Of course, when doing a rewire, most people add things like an electric cooling fan, more fuses, alternator etc so no 2 cars will be identical, but the basics will be similar.
Regards
John