Go have a good look at
Equipped to Survive. They have some excellent articles on ocean ditchings along with raft tests.
Be aware that exiting a high winged a/c
with a liferaft and getting the raft deployed without losing it is considerably more difficult than with a low winged a/c.
Marine forecasts will give you the height of waves and you may want to take them into consideration before committing to flying over those sea conditions.
The offshore helicopter people go through ditching survival courses and you may want to take one.
As a canoeist I have had the odd swim in serious rapids -- wear a survival suit.
With a freshly rebuilt engine, you may wish to fly it at least through the breakin period, maybe even 200 hours -- check with your ferry pilot.