The names Gordon, I live down here in Adelaide Australia & I am presently rebuilding a 256 Y Block to install into my 48 F1 – upgrade from the flathead 6 in there at present 

This is my first Y Block & I have many questions on the rebuild one of which is the choice on valley covers (WITH  or WITHOUT  REAR BREATHER) if I choose a cast alloy one with a fitting for a PCV GROMMET can I then do away with the “Block mounted bake bean can breather” which I am told can get fumie  –
or Do I need a PCV set up or can I just rely on the oil filler cap as a sole breather source? – do I then need to do anything else? is there enough ventilation space from sump to valley to be able to do this? (oil drains and distributor shaft cut outs)

I see a few aftermarket valley covers with no oil filler or PCV Grommet breather – how do they achieve engine breathing (oil filling?)