The model 51 Ranger was built from 1965 to 1979, and was Rover's first Ride on mower. Was essentially a copy of the snapper/ariens/simplicity of the time, with a few Aussie improvements. The one you have there, looks to me like about a mid to late 60's model.
The earliest ones had a angled handlebar, not curved, and they had curved rear guards, not bent. I have a couple of push mowers with that style of throttle control, from that period. Another tell is the side bars on the seat, I have seen those on the 65 ones, but they were gone by 70. Permitting those are original parts that is. Also, the 1969 Rancher I have here has a Yellow seat, by 70 they were red.
The engine numbers will not tell you much as that is not original. Back that far it would have had a white steel tank 7hp, or the early ones were red 6hp with a unusual carby and tank setup.
That is an excellent example of one, rare to see them in that good of condition still. Any rover ride ons from the 65-70 period are really quite rare. It would be great to find a more accurate engine for it, I would be fairly confident in a white 7hp being close.
