2" - 2.25 Exhaust Question /6

Have a question and i do believe i've read somewhere that moving to a 2.25 from a 2" exhaust from the manifold to back end will help reduce engine blowback. The reason for this ask i i've recently had my PCV valve fail and noticed that i had some oil blow up threw the top pan breather cap and possibly top pan gasket itself.

Another question same topic my breather cap is the one with no spigot for a hose it vents out to the top pan. I noticed on later models (mine is a 68) that the breather cap is also hosed back to the air filter. Is there a benefit to have this done to mine? Purpose for this is i'm looking for way to lessen the leakage and i believe there is fuel component benefit there somewhere to. Thanks in advance any thoughts on this greatly appreciated. Jim