No-one mentioned the Grimshaw Revelation yet? This added a banjo-style resonator - effectively a second body - to the body of the instrument, which had a rear sound-hole. The sound emerging from behind was thus projected forwards through the gap between the body and the resonator.

A friend of mine found one in a second-hand shop in Bournemouth around 1971, and we renovated it together; we weren't overly impressed with the use of dowels in its construction.

Charismatic, perhaps, but clearly not a quality article...

RM