I have an old Revell 7,5cm StuG.40 Ausf.G which would seem to be a late version (Topfblende, coaxial MG, remote MG) from Nov/Dec '44 onwards. How much needs doing to it to backdate it to Normandy. I know the coax hole needs filling, but when did vehicles with the remote MG start reaching the front? Mainly I want to get it to Normandy so I can put a waffle zimm coat on it.

It is called "Rundumfeuer MG". According to Spielberger, it was reported on April 3rd, 1944 that 27 of them were already tested at the Front. So most likely by the time of Normandy invasion they were already used.

If it has a travel lock fitted to the front of the vehicle, you would need to remove (or not install) to make it accurate for a Normandy vehicle as well. One other minor detail would be whether it has sockets (pilsen) for the engine crane on the casemate roof...those were added in July so wouldn't be fitted on a Normandy vehicle and should be easy enough to remove. HTH!