I got my slides back today and thought I'd (1) thank everyone for their very helpful contributions, and (2) summarise how it went.
As it turned out, it was raining buckets the day I went, but quite bright for a rainy day. There was enough light that I ended up shooting Provia 400X at box speed. My main lens was an 85/2; I had a 135/4 but generally couldn't find stable enough places to use it. (Contax IIIa and Sonnars, with a separate handheld meter, if you're keeping score at home.)
There's a "no flash, no tripods" sign, although a lot of people were futilely using flash on their digicams anyway without apparent consequence. You don't get terribly close to the actual warriors, so the longer lenses were really necessary. I did find that 85 was long enough to get useful shots into the pits, and while there were times when I wished the 135 was faster, I didn't really feel the need for a longer lens.
What I found most frustrating is that there's not much contrast: you end up shooting dirt-coloured statues against a dirt-coloured background and just hoping that something makes them stand out. In colour the results are OK but not especially dynamic; in b&w they would have been hopeless unless I targetted extremely high contrast. (If I were to go back and shoot in b&w, I'd probably want something like Tri-X in Diafine, more for the contrast than for the extra speed.)
I've seen the slides now but haven't yet postprocessed any of the scans---I'll post some when I do.
Thanks again to everyone who helped me out!