Converting Campagnolo Ergos

You don't need to change mech to go between 8 &9 gears, the gears are closer together (so the range will be similar) and the indexing is done at the changer, not the mech.
The pull ratio between the amount of cable and the amount of sideways movement of the cage is all that matters, and that's the same on all late Campag mechs.

Just fit the right cassette and changer, and set up limit screws and indexing.

Interesting!

You can't fit a 9spd cassette to an 8spd rear hub/freehub, BUT if your 8spd cassette is loose sprockets with spacers (most were) then you can replace the spacers with those from a 9spd cassette and then it will index perfectly. The 9spd cassette will have one more spacer than 8spd, this one you put on the freehub first before the large sprocket. I have a set of 9spd spacers you can have for beer(s)! Obviously the key thing is to get the hi/lo limit screw set correctly, and the cable tension, then you effectively 'lose' the 9th click on the Ergo. I'm happy to help set this up for you if you like (you know where I live!) = more beer :)
p.s. give it a clean first ;-)

There are two different types of 9 speed cassetes/blocks. Is this true of both? If so, that's annoying.

In any case, it does look like they're loose sprockets with spacers (the outside sprocket/lockring is attached to a silver coloured thing-a-ma-bob, where as all the others seem so to have dark coloured spacers in between them).

I am more than happy to get your drunk enough to work on my bike! It does need a clean though. Bah! Hate cleaning bikes.

Oh, and Kris (east_end_images) will have the 8spd Syncros off you, or I will take them on his behalf :)

Ha, these are the Syncros I got off of you. I'll send him a message.