My outdrive was recently stolen.

I have an oportunity to buy a rebuilt outdrive with a 1.47 ratio at a great price.

I need a 1.81. Can I buy the right gears and have them installed? (I have access to a pretty good mechanic.)

Thanks for the advice!

What about just changing the size of the prop might be easier just my .02

yes you can get the right gears, but by the time you pay for drive and gears, you could have just bought the right drive, what size of prop where you running, prop change may be an option.