Richard
My understanding of the Green Glides is that every glide is custom made for each specific wand, so my initial thought would be that no, it is not interchangeable with your Westpac.
Having said that, I recall hearing that the GreenHorn is based on the Westpac low profile 4 jet wand head. If the glide physically fits, it may not be at the right angle. All I can suggest is try it.
Before removal, remove any sealant you may have and try standing the glide part of the head in a bowl of VERY hot water for 10 minuets or so, topping up from a kettle occasionally. When ready to install on your Greenhorn, boil the glide for 10 minutes first, it will be so much easier to install. Don't worry about melting GreenGlides, they need about 500 degrees to melt.
Safe and happy cleaning

The Ken