It is in the carburetor. The fuel line leads to a small well that has a valve and a place for the valve to seat- thus metering the amount of fuel that enters the carb. That kit has the valve and seat. Not abnormal really.

Not sure why you call it a "pressure" kit?
The part # just refers to it as a carb repair kit.

Pressure as in equipped with a fuel pump. These kits Kohler came out with a couple of years back to allow one to service the seats that previously weren't replaceable. The seats are different metallurgy. The kit # for a standard gravity feed is 12 521 03-S. They are pricey compared to Briggs. But, cheaper compared to a new carb- if they get the job done.