So, I knew I was missing something wrt the latches and how they attach to the roof.
The holes I had in the roof were close to 10mm but the bolts were only 5mm with nothing to screw into.
So after a bit of fiddling and investigation I discovered a plate that had dropped behind and sure enough, 2 threaded holes - same on both sides.
Next was the rather tricky part getting them back into position behind the larger holes.
Anyway 10 minutes and lots of swearing later, with the help of bits of string, wire and cable ties, they were in and I could attach the latches.
The original roof liner was missing the foam backing (well in fact it crumbled and disintegrated as I touched it) and was also a bit too stained to reuse directly.
I decided to colour change the liner from cream to a more practical black using vinyl spraypaint and glued it to some self adhesive foam sheet which I'd already applied to the roof.
I also cleaned and filled the area around the latches - I'll probably paint it properly later.
Now what to do with the side catches.
I tried the turnbuckle approach, both with and without the original thumb levers but just couldn't get them to attach to anything securely.
Looking at what was there originally (the one on the right :-)) I bought a couple of J-bolts (M6x60mm), attached them to the original fittings and they worked a treat :-)
As you can see from the pic, there's an angled rod end (reverse thread), threaded joiner and the J-bolt.
They're hooked onto 2 bolt heads tucked away inside and are secured fairly tightly by the original thumb levers.
So, now it's attached and looking great (as viewed from through the rear window).
I do however have a problem...I can't open or close the doors with the windows closed :-)
Maybe just a bit of fine tuning but I fear I may still need to remove the soft top, either completely or at least detach the rear of it to make this work.