Thanks for the comments guys. I look forward to all comments, opinions, and experiences. That is why I am here.

I am hoping to get an opinion from an engine builder as to the risk associated with counter rotation piston rattle. A little start up rattle ~ Like the 200k miles 4-cylinder cars make on cold start when they have excessive skirt wear should be acceptable. Detonation style hammering clatter would not be acceptable.

It's a 25 yr old boat ~ a little healthy v-8 rattle isn't gonna raise any eyebrows. The strait thru at the water line exhaust will mask most of it.
It should see 20 - 40 hrs use per summer ~ generally you don't wear engines out like this.