i'm a bit late on this thread to sorry,but i was in the process of finishing of a tribsa cafe racer, before starting my extension,and did think like john of sharing the petrol and oil tank method,but built my own ally goldstar central oil tank,with a central filler,i've seen oif conversion on the B44 ,and B25,scramblers,done by terry weady,but these frames have the single downtube,before splitting,but i'm sure it could be done,but a road bike needs the oil capacity,you got me thinking now,and i have a b31 framed tribsa scrambler,which i was going to put a japanese engine in,maybe i could fabricate something there !