I have a Brison 5.8 in a Ziroli Corsair and really like it. I'm not sure it would be so good in a very light weight plane. However, I have seen some brute 100cc twins also shake a light weight plane pretty hard. The stronger the twin the more impulse power that is produced.

I also fly a ZDZ80RV in a 1/3 scale Super Decathlon and it has about as low vibration as I've seen in a single. It would have to be my recommendation for your application due to it's light weight and low vibration.

Ken