The twin will fit and I debated about that for awhile and was told by them it can be done but is more enjoyable as a single. I say go for it as I went single and wished I did twin. I had built a 30.5cc equivalent to their bzx4 and at best it hit 35mph at 18,500 rpm. Their prop leaves alot on the table and the hull road very wet in the water.
You need a better prop from prop works west and a bigger engine than the 30.5cc.... I have a run video of it on my channel or on this thread.
Being jerked around means don't expect to get it from what you were told, count on a few months
I now remember
@Nealv had to wait