The Monaco is reported to be based on a 1962 850.
Body needs a tad more work than of 9YaTaH's.

But is the stamping on the firewall original? Has two different numbers. One was under the ID plate, and the other one which looks more dodgy is below it. Are they both original - one from the UK and one Australian perhaps?

The two numbers are correct for an 850 built at that time.

The hidden one is the body number. There was no ~500 difference on those cars.

so the roof really is a separate piece...

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did I tell you that I won a trophy?

There were 2 numbers stamped on the ID plate. One was the Australian BMC Car Number the other I believe was the CKD number. The CKD number was much higher and was at least 6 figures. The very early cars had these numbers stamped either side of the speedo mounting hole and on the floor behind the drivers seat.

The 2 numbers stamped on this car seem to be both the Car Number and obviously stamped at different times (different stamps used) The Car Number on the ID plate should be stamped on the car and can be hidden under the ID plate..

ID plate details and pic of new roof for the Clubman.