I think it's a Murray difference, the air inlet to the carb is way smaller than the opening from the UNI filter. If you look at the first image, the two holes facing up, left the UNI filter, right the air inlet to the carb; those are the parts that need to meet up to mount the air filter. No matter how much I tighten down that hose clamp it's not going to take up that much space to let the two meet.
The stock air filter was different too, I'll have to get a picture of it. It was a sort of plastic cylinder with a metal mesh filter, and had a piece of pipe inside with a small opening on both ends to restrict the airflow.