Note that there are two different styles of crankcase vent tube for the Twin Cam engines. Pictures at right show the early style with the bottom securing clip bolted to the side of the engine block. Notice the P-clip securing bolt is hiding behind the dip stick tube (which is part of the removable alloy sump). This implies that the vent pipe and bolt needs to be installed before the dipstick tube is installed, or before the sump is installed.

Pictures here show the later style vent tube where the securing P-clip is bolted to the engine rear plate. These tubes are different shape, and the engine side covers are also different part numbers with the curved connector pipe at a different angle. These parts are interchangeable only as matched sets.

This next picture is a suggestion for installing dual vent pipes. This is prompted by the fact that Twin Cam engines run with larger clearance for the pistons, resulting in greater blow-by gas flow through the crankcase. Twin Cam engines then use more oil, and leak more oil, suggesting some undesirable pressure may develop in the crankcase. I do not know the source of that replacement front tappet cover. It may be a special modified part. The primary intent of this modification is to reduce oil leakage.