Twin choke Weber manifold - There is a 'T' Connector in the middle of the manifold. One side goes to the oil separator. Where should the other side connect to?

Possibly to a brake servo?

Yep - brake servo.

Presuming that you're not using a brake servo, you can either block the unwanted hole, or get a single pipe fixing (I think Burton Power sell them). Be aware that the old fixing may snap when trying to extract it (guess how I know) as it's very old aluminium alloy screwed into the ali manifold. Not too hard to fix if it does - just drill out the core and pick out the remaining threads - but remember that it's a tapered thread.

David

Wonder where all the petrol went? If the union breaks when you try to take it out cut througth the remains using a junior hacksaw blade very carefully and remove in sections . Got mine out that way