Regarding multitasking support via register-switching (save registers), is it possible to perform a push command to the stack?
Like any other RISC processor, PPC405 does not have dedicated stack operations (PUSH or POP). The software is responsible for managing the stack and saving the link register in the stack segment in memory.
PPC405 does provide all the means to support multitasking; it does have an MMU and a process ID register. To facilitate the saving of registers during a context switch, PowerPC contains instructions that allow a group of registers to be stored to memory.