How do you identify a Factory OAI air filter housing(not the topper.
I now they have the 5 holes for drainage, and the smaller lid.
But what other differences are there compared to the standard non-OAI housing?

 

1970-only had a ~1/2" hole in the underside of the air intake horn on the OAI filter housing (base).

Some 1970 models had vapor recovery canisters. And in 1970 there were three hoses on those canisters. The third hose was a vent hose that went to an elbow installed in the hole on the underside of the air horn.

 

Thanks, unfortunately mine only has the base and the lid. The air intake horn was removed for some reason. My base has two small openings, one on either side, for the dual breathers attached to the valve covers. And there is a thermal vacuum switch mounted in the bottom of the base. Plus the 5 holes for drainage

 

You're right, those dual breather openings are a requirement on a real OAI air cleaner base. However, other cars with dual breathers (such as 4-speed 442s) also had dual openings.

If the decal is original, a 1970 air cleaner base will have an "ON" decal. We had a discussion on here a while back about the decals.

https://classicoldsmobile.com/forums...-118797/page2/

 

Thank you