[quote=Brushwolf;101053]Not sure what this is. Never seen a rear breather for FE.
These were intended for the original Cobra cars & others for Ford racing endeavors as they had "Pent-Roof" or "Bald" valve covers w/ no provisions for breathers. Yes, they install in the rear of the intake (w/ a "basket" mesh filter).
The problem with not having breathers in each valve cover is that condensation (and other by-products of combustion) tends to rise and accumulate here, and without evacuation ads in sludge accumulation.
Also, other variables in your measurements would include the base circle of the after-market camshaft & difference in geometry of the different rocker arms. So, be sure to physically measure for adequate clearance. Scott.