The Swallow is a good all round plane. There are a few structural issues but as long as you are aware of them they are easily surmountable. Do a search for it in this forum, there is no point repeating it all here...

If it was me with this engine I would mount it at approximately 45degrees and use the standard silencer (ie with the silencer along the centre line of the fuz). This will be a whole lot quieter and won't restrict the engine as much. It also will allow you to easily fit a pipe if you so wish in the future, without the need for expensive swan neck manifolds. Also with the "flat four" style cowling it will be the least obtrusive this way, too.

James