Just spoken to Meena at GD Cars. Committed to buy a GD427 kit. Small deposit to pay when I get the paperwork. Looks like the body will come first, followed by the chassis, probably in Q3 of 2015. With a GDJag chassis it is often the other way round.
I will go for a Mk4 body with a GDEuro chassis.
GD cutaway view from GDs website
So now the wait for the build. Plenty of time for further research!