I found a very complete article (two articles, actually) on replacing the tensioners, guides and timing chains on Jaguar V8s. It has many photos, which are very helpful. I read enough to know that this is probably not something I want to try to do myself. I could probably replace the upper tensioners (with the proper tools, of course), but doing the whole thing looks pretty daunting.A local repair shop with Jaguar-trained technicians has quoted me a worst-case price of around $3,800 (presuming everything needs to be replaced).

Here is a link if you want to look it over.
http://www.jag-lovers.org/cjw/#0104a

 

I'm not going to take this on myself. There is too much to be done and the stakes are too high.