The Type 89 grenade discharger (knee mortar) may see even more varied use than OTL. A HEAT round could be possible, though only 50mm in diameter, it might just be enough against the sides of Allied tanks.
That said my knowledge of Japanese HEAT research is less then zero.
The Allies seemed quite...
I wouldn't mind seeing the Fairey Battle getting a second chance so here's a few ideas.
The Costal Command Battle, fitted with a standard aerial torpedo and under wing drop tanks.
The Royal Navy after seeing the success of the Costal Battle start testing a folding wing, carrier capable Sea Battle.