IMHO it really comes down to how close to your natural potential you already were @ 400 , how hard/not hard you've really worked on your deadlift previously and what level of focus you are willing/capable of bringing to this goal.
Even then there's no guarantee you will reach it in time but man you've gotta respect the kind of guy that would go for it balls out and do everything possible to train to achieve it.
here's some suggestions(none of which are meant to do anything but say "hey if your life depended on making this lift here are some things you could do"

:
- It is quite common for certain body types to very quickly add 50 or so pounds to their deadlift simply by switching to sumo.I experienced this myself sometime ago and hear/read about this happening all the time on the intardnet.This would require a time investment of learning the technique as sumo is much more technique driven. There is no guarantee that you are one who is better suited to this style though...
-(this one although offered "tongue in cheek" WOULD actually be a huge step towards the goal) invest in an order of Finaplex from a vet supply company- contrary to "bro" lore , you can see results if taken orally (crush up the pellets as finely as possible) especially if you are very responsive to anabolics (ie. never used before) , again there is "bro" lore and there is reality , these days even Patrick Arnold (prohormone Guru) admits oral delivery will work - just less than transdermal and injection . - transdermal IS a better, more potent option , just order the gel to mix it in (DMSO) readily available on line and just 2-3 finely crushed pellets mixed in is simple , as legally no risk as you can get and needle free. You WILL need PCT if you intend to have sexual relations requiring an erection anytime in the 3-4 month period after stopping use!Also some bail money set aside is a good idea if you tend towrds aggression in any way...
- drop military /overhead press and any row where the back is unsupported (chest supported rows highly recommended instead)until after the 500 attempt these tax the lower back and are not the best training investment for your goal. Squats and deadlifts are. Use this idea on your entire program - bench for instance isn't going to have carryover so "de-prioritize it".
-eat everything and anything between now and then, if you get fat F@#K IT! lose the weight after the lift...
- Since the lift is on the 18th you could intentionally overtrain between the first and the eighth then take off completely the next nine days. This should be assessed as an option with an eye towards how intentional overtraining/ compensation has worked/not worked for you in the past.
- you're going to want to taper down the reps and increase the load over the interim weeks - anything over a triple during the month of may prior to the lift is a waste of time and CNS resources.
- Invest 100$ in a Titan deadlifting suit you can wear it under some sweats and your buds wont know a thing!
Of course you could do all this and still run an incredibly high chance of not reaching your goal in time - but hey one never knows their limit until they've attempted it...