While fuel costs will be greater for any given sector on the 748 than the ATP for example (I believe the former burns around 1100 l/hr and the latter 900 l/hr), the fixed costs will be much lower. For low utilisation contracts or ad hoc work Janes should still be able to offer attractive rates for that reason, plus the fact that they should be able to run a lean, efficient operation given their experience with the type.
I say good luck to them.