Hi,
Have done this on 2 cars,
First was via the process listed on here years ago, downloaded firmware, downloaded updated map.
This worked fine and at the time I ended up with a version A running firmware 2760 (which gave the full postcode search) and latest map at the time.
As you have realised the HDD is smaller and the dvd drive is not dual layer on the A model.
So the golf I have now also has an untouched version A.
I took the plunge and bought one of the kits on the well known auction site.
It consisted of the latest possible firmware (for version A) on dvd. A special loading disc and map data on sd card.
Basically the firmware updates first as normal, taking the sd card limit to 32gb, Then you run the loading disc which makes the unit take map data from sd card rather than the dvd drive. The bigger sd card capacity can handle the newer bigger map data.
It worked well. The old A unit now has much newer firmware and 2019 maps. Cant remember exactly which versions but I can check for you if you like.
Good luck with it, support for the older versions seems to be running out.