I had a Sonic 33', not alot of 33' sonic made. The boat had 454's with mx07. You can still get parts, they are pretty easy to work on. They looked cool as hell, it was hard to find props, I sold the boat with 2 sets. They still make brand new drives. Just not mainstream enough to get anyone to buy them. They are used by the military and are used for pleasure boats in the UK. Most are now being applied to diesal motors. I had them running with 425HP a piece. The manual that I had said they would handle 800HP. These were older. The sonic was an 81. The motors were new and so were the velvet drive transmissions. The new ones that they offer supposedly can handle 1100 HP from what I heard. They take a ton of Outdrive Oil. But they do run cool.
The only problem I see with the drives is the resale value if you decide to get something else. People looked at them and said, what the hell are those.
Just to let you know they will do full rebuilds of the drives. I would do them in the off season, since I don't know what kind of turn around they have.
Just my 2 cents