I would not use a filter; it'll only clogg up and make things worse... been there, done that... If there is blowby oil after you vent to the carbs, it will not clogg up the carb because of where it enters the carb. It'll just mix with the gas as they, combined, enter the intake manifold. ...
The point being, if you do relieve the crankcase pressure you are not likely to have as much oil blowing by because you won't have excessive crankcase pressure propelling it....
Just try it. Don't dismiss it until you've tried it.