Not sure what’s going on here

It looks like a Chevrolet engine which means its in backwards. Further proof is what looks like a starter at the bottom front of the mower. That goes at the back of the engine. The headers bolt on in whichever orientation you want so that’s fine, but there’s no intake at all, the heads are just open, so it cannot possibly run.

Regardless the mower was designed to work with a vertical shaft motor, and I don’t see an obvious gear train or pulley to convert the horizontal shaft of the engine to work with the mower.

My guess is that it was just set in place for fun, but hot dang that would be a fun project to make work.