If I am wrong please correct me you can dive lnrc into bridge ?
Can you then drive to town drain ? I assume once your in town drain you cannot dive to the white lady ?
No and no.
Back to the question of kit configuration, having now read the book, back mount might be OK if just going from White Lady to Pwll y Rhyd, but definitely not for a dive up to White Lady 2, which involves "two intimidating extremely muddy bedding plane squeezes".
Perhaps best to familiarise yourself with the sump on lightweight side-mount setup before lugging filming kit in?