Ok I managed to find an hour to install them today. I wanted to use the correct wiring so had to take a few interior panels off to get to the original rear speakers and remove them completely. I re-used the nice little connector and soldered the other end onto the speaker boxes so that they can be removed by unplugging them easily and all original wiring is in place.

The sound is a vast improvement. Must more depth and can now take a bit of volume. If I am honest there still isn't the "bass" that I am used to, but I drive a modern Skoda with fancy surround sound system and subwoofer, so I am probably being unrealistic expecting anything like it!

Next job is to cover them when the material turns up, and then I'll take some pictures. I might upgrade the headunit for one with bluetooth as I like to stream from my phone, but I'll make sure it is all reversible so I can put the original unit back in if needed. Something like this would be good https://www.kenwood-electronics.co.u.../?view=details

I would call this little job a success