essentially a 763 is a 763 without regard to where it flies.

you might get NGBC seats.. you may not (100% is supposed to happen by end of 2007).

I did SCL this summer with one way NGBC and one way old seats (cannot tell even at the AC prior to the flight).

Don't worry. The inflight service (at least on my ex-DFW flights) was excellent in J.

Latin American 757s are also the same as domesitc Us 757s

BTW .. I do not think AA ever flew 777s to SCL which would be your only 3-class option.