Having asked questions of InCarTec tech support by email and getting zero response I decided to bight the bullet and try the 39-VOL-01 interface.
The great news is that it works with the car and the Android radio
If anyone else is changing radios and wants to keep the steering wheel controls the 39-VOL-01 says it works with all the mainstream brands of radio eg Pioneer, Sony etc plus Chinese brands like Xtrons and Zenec.
InCarTec also make a 39-VOL-02 interface, essentially the same as the 01 but with another lead included for cars with a separate factory power amp.
I know it's a bit late in the day for updating radios in a 21 year old car but I really like using Google for navigation, having it on a bigger screen and built into the car is worth the effort for me. I had navigation on my old Pioneer radio but keeping the maps up-to-day was getting more and more difficult and costing a fortune for maps that were never quite current.