Okay.....no cork.
Was that part of the removed emissions control stuff? Manifold vacuum?
On US water pumps, often you will get a Corbin Clamp and a rubber cap, to cap off unused heater hose lines on the generic pumps.
I think I still have one or two around here somewhere.
Will a 1/2" or 5/8" piece of heater hose fit over it?
If so, see if your local parts place has one (looks like a rubber thimble), put a flatwasher inside to keep vacuum from pulling the end in too far, and push it on. Since no pressure, probably won't need a clamp, altho some sealer inside before you press it on would be cheap insurance.