Yes Ross, you can put in anything, as there is no force on it.
I have put Epoxy in, but also some piece of left over rubber or silicone adterwards.
You also can cut off that 'kickstarter spring holder' from thre casing
and leave that metal plate on top of the clutch axle bearing if that was on.
Somehow that RD/TZ casings were 'over-engineered' and a lot off parts
are outdated or un-necessary.
It's actualy funny that a TZ engine with a straigt cut primary gear have four clips on the cranc, where a RD has only one, does that make sense ??