How long before you need them should you ask for letters of recommendation for academic jobs? I've heard the etiquette is to ask 3-4 months in advance, but haven't found much corroboration for that. Honestly, that seems like quite a long time. Would asking as late as 6 weeks in advance come across as rude?
I can't speak for everyone, but 6 weeks would be fine for me personally. Less than 2 weeks I'd be grumpy about, if there weren't a good reason.
I would like a month or two advance warning, because a coherent, helpful letter requires at least a half-day's work, I think. EDIT: and, just to explain, usually all my days are over-committed (note: over) several months in advance, so it's not that I can happily re-allocate any significant part of a day on short notice.
I also do not think that it's about providing other material, because I strongly think that my letter should refer to my first-hand experience with a candidate. After all, their transcript and other activities that I've not seen myself ... will be documented otherwise... and my comments on such things will be worth nothing, in fact, contrary to many traditional beliefs. That is, my praise of a transcript means... srsly... what? Or praise of a summer project, or other projects done out of my sight, etc?
I read letters, on our grad admissions committee, and I write letters, focused on first-hand experience, NOT on commentaries on transcripts. Such commentaries add nothing.
Therefore, there is scant point in giving your letter-writers your larger CV... although it is traditional. If (heaven forbid) all they can do is wax eloquent over the wonders of your CV, they're not adding anything, not helping you.
(But, still, apparently lotta people can be fooled lotta the time. Still, further, I myself would not want to count on fooling people.)