Congrats on the major new 400 PR! On paper, you are looking like a 2:02 guy. Don't sweat the 800 on the double, the 400/800 is a brutal double even with decent recovery time (curious what your 800 time was though).
NOW... you are looking down the barrel of five races in six days. This is a big mistake. Your 800 on Saturday sounds like your best shot at a good PR. Use tomorrow as a workout, if possible only run one of the races, and negative-split it significantly. You should go out easy and blast the last 25% of whatever you run. On Sat go out more aggressively, like 60-flat for 400, pace through the backstraight, and hold your form and work your arms the last 200. You might even sneak a 2:01 if all goes perfectly.
Non-race days only easy running, strides, drills and maybe a mile or two at tempo (5:30-45 pace).
Good luck and again, congrats on sub-55.