The more breathing the better!!! Some blocks have the hole in the side for the mechanical pump, if not, You can make one.
 
A lightweight (72g) high quality crankcase breather take-off in 5/8-inch size to fit the standard mechanical fuel pump location.
 
CNC machined in the UK from billet aluminium.
 
Anodised in silver and supplied with a new gasket, fixings and even the Allen key.