Ki48b seems to be usefull imho. It's the only armoured bomber that Japan gets before 9/42 (when the Helens IIa comes online) and you already have a factory producing the Ki-48a (so no need to spend HI, mpw and supplies to change it).
It's true that it has less than half bombload than the Sally or the Helen, but it has decent range and in backwaters it can be used in many roles (ASW platform, airfield bombings in China etc).
In the first months of war Japan is always short of Sallies and Helens and, if you don't wanna spend too many HI and supplies to bump the Sally production early on (with the problems related to the mitsubishi engines too), the Lily is a fair alternative imho.
Personally i produce, in mid 42, 80 Helens Ia, 40 Sallies IIb and 40 Lily IIb (which is proving to be more durable than the Sally or the Helen, with far less pilot lost due to flak) and i feel these numbers are ok