How can I tell if my installed Android version, not CPU, is a 64 bit or 32 bit one?
uname -m will display the architecture of the running kernel.  This is different than whatever your hardware may be capable of running.

Unfortunately, you have to know which architectures are 32-bit and which are 64-bit. But you can easily find this out.

For example, my m7 displays arm7l. A quick search confirms that this is a 32-bit architecture, meaning that my running kernel was compiled as a 32-bit executable.