Consider DIY. Boats are easier than you think to swap motors.
There are a TON of sites to go to and get help if you have any sticking points.
The biggest issue is lifting the motor out if the boat. You will need a tall engine lift to get it out.
FYI, if the block is cracked, a complete rebuild is not worth the money
If I was your neighbor I would come over and do it with you as these projects are fun AND you get to save a lot of money.
Be careful with rebuilds as you need to know what was "rebuilt"
Check out
www.marinepartsexpress.com. There are many sites but this one is fairly reputable.
Now it a time to consider upgrade to 4.3L as well..