Hi Turb.
One thing i will say about levellers, they need to pretty responsive, the bigger the boat, the more sensitive and responsive they need to be. For example, on a small boat of say four feet in length, you need a responsive and undamped leveller to cope withit, you can toy with the sensitivity contol until you find a best, fits all, setting.
On larger boats these units have to very responsive indeed if they are to cope, another example is the huge Los Angeles clss sub, originally designed by the ingenious Dennis Cater of Eden Models. When I used that boat, it needed a self leveller so sensitive that it was virtually twitching all the time, if you so much as tapped the sub it would respond quite vigorously and aggressively with big inputs to the control surfaces.
The longer the sub, the more sensitive it needs be. There is a lot of inertia in a big sub and it needs a big input to correct even a small change in pitch whereas with a much shorter sub the movements can be slight and a bit slower... but they do have to be pretty responsive, I have little or no experience with aircraft gyros but I believe they are damped somewhat since aircraft are obviously lightweight and do not have a mass and inertia problem such as that found with subs.
It will be interesting to find out hoew you get on with this experiment. Good luck.