More power from the standard engine?

For a 1300 twin-cam, the Jimny engine is not particularly well-endowed in the bhp department, ok,this would not be quite comparing like with like as the measuring standards are different, but the old Mini Cooper of 40 years ago was 1275 and claimed 75 bhp. What would it take to get another 20 bhp? The only real mod that seems to be available is a change of exhaust manifold. Here there is a choice: Janspeed, K.A.P, or Rhinoray's...have any readers personal experience of these, do they make a noticeable difference, and is it worth doing...

Is there anything to be gained in junking the fuel injection and fitting a carburettor to a 2005 low-mileage Jimny, on the basis that the current set up is presumably one primarily for good torque, reasonable fuel consumption, and of course emissions.