The pushrod 253FMM does not have a cam chain, but it has a cam gear with specific timing marks. Lining up the "O" and "I" marks on the gear with the cylinder head is impossible without the diagram.
While a single "universal" 253FMM manual is rare, you can access the necessary technical specifications and procedures through the following official and community resources: 1. Primary Service Resources 253fmm service manual
Use these as a guide, but verify with the manual page specific to your model year. The pushrod 253FMM does not have a cam