I really love these bikes, very unusual, thanks for sharing.
I remember having saw a Harley engined with a Vtwin coming from a Rolls-Royce V12 taken from a RAF 4 engined bomber, can't remember which one.
I'll try to find it back to show you.
Can't find back the magazine with the picture but not sure it was a Harley now after seeing this : Lucky Keizer's big twin
In my memory it was a 1100 cafe racer based bike, quit similar ... but I remember a secondary belt transmission ... not sure.
In the original cliche the monster was presented in front of a black under surfaces painted Lancaster (City of Glasgow ?), that's why I talked about a 4 engine. Very impressive combination.
I found this while searching ! Leonhardt 410 Cubic Inch V-Twin Motorcycle - The Kneeslider
410 cubic inch Vtwin, Boeing tyres ...
Where is the kick ? Eh eh.