By all means, use a reputable prop shop.
They will provide you with a sheet with tons of questions, transmission ratio being one of them, so start digging in your files, and polishing up the tags for info.
Another hard but critical question is boat weight.
The OEM propellers are likely not what you will need, though it will give you some idea where to start.
Also make a chart of the performance with whatever props are on now, log engine rpm at 100 rev intervals across the range and plug in boat speed, engine and exhaust temp and manifold pressure if available. (With clean bottom and running gear)
Check to make sure the engine is capable of making rated rpm in neutral.
If it won't, fix it before attempting to select new props.
This will all help your prop shop select the right prop for your rig.
If you'd like to understand more on the subject, I would suggest reading Dave Gerrs "Propeller Handbook".
You can lead a horse to water,
But you can't make him ski...