As you may know I think I went through 4 or 5 variations of tanks and breather systems till I worked all this out below.
Took some pics for you yesterday, sorry for the delay, here we go.
The specially made restriction (ok it was an aeroquipe fitting I had laying around
) drops down inside the primary filler neck.
This sits far enough in that any oil washing over the top of the inside of the centre iron goes back into the sump and cant wash up the secondary part of the filler neck,
(the restrictor goes in then the secondary part of the filler neck bolts on with the two 6mm bolts),
Next I put a small piece of fuel tank foam into the filler neck before the cap goes on.
Next after playing with various hose sizes I settled on 1/2" id (13mm) for the one and only breather to come out of the engine back to the catch can.
The can now has no baffles inside and as you can see marked with an X, "if" any oil that goes into the can it drops back into the engine anyway.
You will see from the pictures I have two breather pipes ,marked with an O, ( this could be just one big pipe) the idea being that the outlets add up to being bigger than the inlet to stop any pressure build up.
The two out lets run the whole length of the car and exit at the rear valence, this way if any oil did come out it would no go onto my tyres.
Now just using a stock sump and filling between full and empty and having no more surge issues