It works!

I just had another go at the Monstrosity and managed to get it sounding better. The bass and guitar strings are now much more in tune and it now makes some interesting sounds.

Given it's demented combination of parts hacked together in most un-luthier like ways, it sounds quite decent. The bass strings sound OK given that they're 10" shorter than they should be and the doubled guitar strings gives that nice chorus effect that I liked so much on the mandolin. I think if I could get a better pickup and some shielding in there to get rid of the buzz, it would sound much better.