Sierra diff as bevel box?

[ROD]

For a single rear wheel trike with inline engine up front....basically..
 Prop from g/box to sierra diff. One side of diff has brake disc attached,the other has a sprocket. Chain from sprocket to rear wheel. I thought the MSVA manual said the brake must be direct on to the wheel and not through a chain? Can anyone enlighten me?
 
 Failing all the above... is there some sort of a ratio'd bevel box that could be used to transfer the drive from a inline engine to a single rear wheel,or is it down to changing sprockets to set ratio?

[snafu]

I cant see the difference between chain drive and prop drive, Isuzu truck and Mitsubishi trucks 7.5 tn and Disco 2 all use a transmission park brake mounted on the rear of the transmission, although accepted by VCA & VOSA they are actually crap, well the disco 2 is ok.