OK, got it sorted now... took the tensioner and exhaust cam out, moved the chain along a link and it lines up perfectly now!
Some learning experiences not documented elsewhere, maybe obvious to everyone else, but not obvious to me at the time!
The gold links do not line up with the cast marks on every rotation of the cams (really should have been obvious because the chain is a lot longer than the circumference of the sprockets!). This confused me because the original chain looked 'wrong' because I was expecting to see both the gold links at the top, instead they were completely the wrong side of the chain.
1 out of every 2 cycles of the camshaft, one of the cast marks actually aligns with the 'inner' link (so appears in between two outer links). On the next cycle the marks will align pretty well exactly with the middle of the outer link (just like the workshop manual picture).
Both of these things confused me when putting everything back, because when I took the cams out they were in the odd cycle, so it looked like the exhaust cam mark should be 'out'.
Measuring between the cast marks I got 112mm, pretty close to what the workshop manual says. So I would say 1mm out = margin of error, 3mm out = one tooth out!
The other detail missing from the other guides is how much of a pain getting the front bridge off is. I drove a plastic scraper between the two parts to get it off. I would strongly recommend (if not using the special tools to remove the cams) to take the front bridge off first and then use the single bridges to let the cams out.
Taking the bridge off completely first means you can eyeball the thrust bearing surfaces in there. It seems like the big danger when taking the cams out is that they won't come up level and then the front ends will bind in the thrust bearing and either snap or gouge the soft aluminium head. If you are at TDC #1 there is a tendency for the cams to come up at the back first (because all the cylinder 1 valves are closed), especially if that front bridge is stuck.
Now hopefully just a few hours reassembly from turning the key!
