WE fervently hope Barnum promoter James Cundall is not promising more than he can deliver. He sent us a communique yesterday to the effect that he would soon be, er . . . exposing ''the greatest organ on Earth''. With the truly impressive dimensions he goes on to detail, we do not doubt this claim for one moment. But then Lunchbox Productions director Cundall goes on to boast about ''priding himself on giving the public something they hadn't seen before''. Further on in his missive, Cundall gets us confused, for he then goes on about the 112-key Gavioli organ which will be on public exposition at the Cultural Centre on November 28. But we fail to see the relevance. Incidentally, apropos Lunchbox. The revealing skintight shorts worn by international track stars such as Linford Christie and Carl Lewis are referred to in British tabloids as ''lunchbox shorts'' because, we are told, ''you can see the goodies on offer''. Any connection, James?