if you don't get a response in a few weeks HMU. I'm going to pull the trigger on a M3P in the coming days as my dual motor was just classified as totaled and like a smaller wheel. Actually was wanting to go with 18's but not sure if the OEM ones will fit over the P's bigger calipers. Maybe we can work something out.
To answer your question, sorry, yes, the 20" wheels will fit a non P model.