ok so after some digging around today and taking measurements I need an engine with a length not longer than DLE20 i.e. 135mm because the engine has to be mounted with the prop hub 150mm from the forward fire wall.
The cowl diameter is 22.5cm so I have 11.25cm or 112.5 mm of space before the cylinder head meets cowling.
Based on those dimensions the MVVS 26/30 SP IFC/RC engine is the energy converter of choice. I think I will opt for the 30cc, I like power in reserve. Also the exhaust options require less modifaction that other engines to allow for a scale exhaust exit on either side of the cowl. Also the beam mount of the 30cc IFS/RC is perfect as it allows as little rework of the firewall.
Will be placing the order by the end of the week.

Plane will require around 9 servo's. I am doing the math on a S-Bus set up for this as I am seriously considering E-Flite worm gear electric retract units or similar. I was planning on using simple high torqu analogue servo's but I want the staggered and slow retract action so the best way to achieve that is via the retract servo units.

Busy uploading pics of the basic ARF and wil have them up in an hour or so.