Aftermarket Air Filter
I've never been a huge fan of the filters than come stock on these engines. They do especially poorly dealing with alternator belt dust and the $2.00 replacement foam element costs more than a good after market air filter.
I have been installing the K&N brand on these engines and they work quite well.
M-25 Air Filter & PCV Fitting
A K&N RU-2450 Air Filter.
On this filter I routed the PCV hose into the bottom of the K&N with a brass hose barb..
M-25 Air Filter & PCV Valve