Unfortunately these types of task fall on the guy that wants to try it, and is sufficiently motivated.
Perhaps diff the sources?
Perhaps review the CM3 vs CM4 nuances that it might be using?
Most likely ported to the L4 because the L4 IoT DISCO board is pushed heavily for AWS usage.
As someone who has ported stuff between a wide range of STM32 parts, and library iterations, and frankly a bunch of ARM and RISC platforms, it is not that hard.
