[CMOTD]

I don't think that Mabuchi is original Leo, looks like a transplant from a Scalextric car. The wires are thicker and different colours to those used by Airfix. As far as I know the Johnson 111 was standard fitment. Here is one from a recent eBay listing.

   

I have found the missing motor from my Lotus and that is also a 111.
I could also be wrong though, I often am. Agreed they do look slightly bulky but total scale accuracy was not that common back in the day.