Most air transfers of Neonates in the UK are emergencies and usually facilitated by ARCC at Kinloss. The RFDS in West Australia uses Pilatus PC12s and Beech Kingairs for transfers. Both types of aircraft have to be multipurpose adult/child/neonate passengers. May I suggest you contact them as they are the real experts in medevacs? The
RFDS Western Section covers the greatest area. Peter Northover used to be the General Manager but I'm not sure if he still is - he may have retired by now.
You also need to look at whether or not you are providing the incubator. If you are, then it must have a means of anchorage compatible with standard ambulance fittings. The CAA should be able to advise you about their safety requirements.
The weight of such incubators before any essential medical equipment is added to them is considerable - from memory the Draeger transport incubator weighs 15 stones or more. I'm not sure what the Vickers equivalent weighs. Hope this helps.