The heating is also dependent on driving style i.e. the harder you drive it, the more heat you will get.
Probably not the wise move. When I had J-tubes I fabricated some tin to extend the existing under-tins, over the J-tubes to the heads. My heads had M6 threaded screw holes in just the right place, though they were after market heads and not all heads are the same.
Hi Graeme, Your bus looks great. Mine is same reg and top, but getting it into similar state seems a pipe dream! To be honest, I fancy your colour too! (Niagra Blue?).