I have that wrong Norm ,the Rover 20 / 21 have 3 outer bolts for the boss and the Rover ride on has the 4 outer bolts.

A guess would be a seventies Rover Ranger / Colt. The centre hole looks larger in the after market plate though.

https://www.[Censored].com.au/r...N7dqf7gIVCJ1LBR2JqQhGEAQYASABEgIIpvD_BwE



Cheers
Max.