<VV> RM engine in early production Corsa?

[john miller]

I got a low number vin 65 Corsa that has an RM suffix code motor (pre christmas 64). The books show RB as corsas only. Just trying to figure if this could be a factory possibility that they also used RM engines in Corsas or rule that out completely and assume the motor was switched out of a Monza or other. And yes I checked the VIN and it is a Corsa.
 
John