Kanzaki KM2P rattle noise (i think) & gearbox ratios?

[UK-WOOZY]

Yanmar 2GM20. kanzaki km2p gearbox. Mine is making a rattle noise. Iv changed the drive plate for new thinking it was that. Concerned it's something bad. Would a 2.62 gear ratio work iv seen for sale, mine is 2.21 gear ratio. Thanks#

 

[UK-WOOZY]

Does anyone know if i can run the engine with the gearbox disconnected as that will allow me to see if i get the noise still. thanks