you have not provided much information.

to change from Kawasaki to Briggs, you will need to provide crankshaft size and orientation, and details of the charging system. There are also unknown details concerning clearance. The exhaust system would probably need to be fabricated. The person who converts this will need the mechanical skills and fabrication skills.

Briggs offers the 386447 with 1 1/8" horizontal crankshaft and a 16 amp charging system. This has 23 hp and is also available with a vertical crankshaft. This is suitable for commercial use.

If you are thinking used, there are many of the consumer engines from light duty mowers (Sears, Lowes) that could be salvaged from used equipment. Most of these will probably not have the correct charging system or the larger crankshaft.

You might try looking at sites that have formulated their own re-power recommendations, like smallenginewarehouse.com. They have a re-power section based on the brand and model of mower you have.