China never acquired the 2A46, so it would be a little hard for them to install it on the 96A. Besides, maintaining two different types of gun would be unnecessary complicated.
ZPT-98 can come in different lengths, IIRC L50 and L48 have been put in service.
The main difference between 99A and 96B is that the latter is much lighter and relies on ERA to be able to tank it’s own rounds, so it’s more like a Russian tank.
Ah perhaps the L48 is on Type 96 whereas the L50 is on Type 99s. I don't know if China has ever formally acquired 2A46 but I recall reading plenty of online sources suggesting Type 96's main gun is derived from one. Maybe from T80 trials and imports or from Ukrainian suppliers? One of the Ukrainian main guns is also derived from the 2A46. Not to mention the two guns looks identical down to the thermal sleeves and fume extractor details.