[Mr Gazza]

The later models did have a pin to stop the rod spinning, but the length should be the same.
That rod is sold for early and late models with the same length rod, but the earlier models didn't have the slots in the slave to accommodate the pin, so it's just a simple matter of knocking the pin out if your slave is slot-less.
However if you have an Oberon slave, it should have the anti-rotation slots in it already, so you can keep the pin and and enjoy the benefits of a non-spinning rod.

If you are using the small spacer piece that comes with the Oberon, remove it for the pinned rod.

I would advise changing the bearing in the pressure plate at the same time and also check the condition and fit in the bearing, of the top hat that the pushrod fits into. It should have an O-ring in it, which gives a bit of resistance when you push the rod in, and also when you try and pull it out.
I always lube the inside of the top hat with Moly-grease, but beware of the Moly-worm escaping from the tiny hole in the end, as you don't want moly-grease on your plates.

Edit.... The pin must go in the slave end. The pinned rod can only be fitted from the slave end, so removal of the slave is essential to install.