I had some experiences with a 1946 RMA Riley, Ian.
Bodywork let it down, as did the rear springs which needed resetting, and poor brakes. The good stuff; engine, based on a 1929 Kestrel 9 (hemi, twin cam, short push-rod) was quite an advanced engine and produced until 1955. Good gearbox, final transmission by shaft-in-torque tube, had no troubles with the oily bits. "Performance" given as 0-60, 25 seconds.
Interesting engine in your Rover, (don't laugh it's a side valve) quite efficient it seems, looking at the data, and adaptable throughout their range in the event. It's a new one