Easiest will be to use another 470.
A 3.0 will require remaking t front mount. A V6 will require new side mounts.
If the boat is 15-18 ft, the 3.0 will be fine. However it is about 140# heavier
If the boat is 18-21 ft, I would go 4.3 minimum
With a bit of looking you can probably find a...