How to play against much higher rates players
I don't know man , 600 points it's just to large of a gap to recommend something. Plus only a few days !
Try chess 960 it will improve your overall vision of the board and increase your tactical vision.
Yeah, 600 points is too much. Somewhere around a 400 point gap means (to borrow a quote) you're not playing the same game, it just happens to have the same rules (so to speak).
If you spent something like 50 hours memorizing some crazy gambit lines, and 1000 hours solving tactics puzzles, and then if you were lucky enough to have your opponent accept the gambit, and lucky enough that they were having a bad day that day, then maybe you could get extremely lucky and win.