Late model Mk1 S cars used the AEG573 manifold.
My late 68 build car had this manifold from new.

RonR

Remove the carbs and check how the centre bottom stud holes have been blocked off. If hex-headed grub screws then it's likely it came from the factory like that. The Police SPO41 specification included CCV instead of PCV for crankcase breathing. I see your carbs have the CCV breathing tubes blocked off.

No grub screw in the bottom only in the top

By the way, the first MK II Cooper S with the performance modifications for NSW Police known as SPO41 was YG2S4-2372, delivered in September 1970. So no Mark 1 Cooper S and none of the early MK II's for NSW Police were SPO41. They were all stock standard performance-wise. The only difference from showroom versions was lowered seats, reversing lights and racing disk brake pads.

The Police SPO41 specification included CCV instead of PCV for crankcase breathing. I see your carbs have the CCV breathing tubes blocked off.

Hi Doug,
What does CCV stand for?
Brian

The SPO41 specification in 1970 may have been the first opportunity to introduce CCV (Carburettor Crankcase Ventilation) into production.

CCV is dead simple. The fumes go up the hose from the oil separator at the back of the engine and into the body of the SU carby where they are sucked into the combustion chamber and burnt. The twin carby models utilised a Y piece to separate the rubber tube so as to feed both carbys.

There was no provision on the normal Mini SU's for the breather tube so introducing CCV would've required a change of carby type. The carby specification for the Police HS4's was designed for just that application (the SU detailed specification sheet for AUD488 is called NSW Police) so HS4 carby bodies with this provision could be specified, doing away with the need for a more complex PCV system.

Later Clubman models moved to CCV along with other environmental design changes.

So perhaps it was just a timing thing with SPO41 cars providing the first opportunity to introduce CCV into the Mini range.