interesting question for me as well - the 1275 I'm building has the two oil separator/breathers and I've also got some sort of valve on my inlet manifold (on the right) as well as the servo vacuum port.
Should I remove the valve and vent into the carbs after joining then separating the hoses to balance the flow?
Your Carbs have the CCV Ports and your Inlet Manifold looks like it has either a PCV or it could also be a non-return valve, as used with some Brake Servos, fitted to it.
To me, for Crankcase ventilation the CCV wins out over a PCV. If you think about why these systems are here and how each works, you'll see why.
Your engine will (or should !!) have the highest blow-by under wide open throttle and that's where any crankcase ventilation needs to work (or flow) the most.
OK, so what happens to Manifold Vacuum under wide open throttle?
And how much Air is flowing through the Inlet system under Wide Open Throttle and also Cruise (& Idle) conditions?
The CCV Port(s) don't work on Vacuum like the Manifold and PCV does, they work on flow rate, ie, the more air flowing through the Carb(s), the more they 'draw'.