I really do not understand why PLA borthered to improve such an old tank. If it is true, one explanation is that, it is for Taiwan. Taiwan is not suitable for heavy tank.
I just wanted to note that the turret looks to me more like the one on the Type 63A, not the SPG. It's probably a prototype for an upgrade that would only go somewhere if the overall cost benefit makes sense, and don't forget logistics factor in. Are the guns on the original Type 63 and Type 62 the same? Either way it would make sense for both types to get the same turret/gun upgrade if they are to be kept in service.
A recent article in tanke Zhuangjia Cheliang explains about the updated Type 62. The 105mm turret from the Type 63A was fitted to the Type 62 but it was decided to make the Type 63A the PLA's new light tank. They are amphibious and it also means one less vehicle type.