We are getting conflicting information on using a higher gear ratio on the lower drive unit for our Volvo Penta lower drive unit.

The boat is a Chris Craft year 2000 308 Express Cruiser
twin 5.0L gas engines
Volvo Penta sx-m 1.51 gear ratio lower drive unit

The lower drive unit has corroded and may need to be replaced. We do not want to purchase new lower drives and would prefer something rebuilt. We are getting conflicting information on being able to use a lower drive with a higher gear ratio 1.66.

The person selling the rebuilt lower drives says we can put the 1.66 sx-m lower drives in with no issue, requiring no change to the prop, and will not cause any issues with the engine.

The person that will likely do the work says at a minimum the props will have to be changed and that the engine may have issues with the higher gear ratio. I assume the boat will run at a higher rpm to get on plane? We usually cruise the lake at 3400 rpm with the 1.51 gear ratio.

Would appreciate any advice on this and also does anyone know a good place to get rebuilt sx-m lower drives at the 1.51 gear ratio? the 1.66 seem easy to find but not the 1.51.

Thank you,