my kei office s13s are a lot longer than the x73s though i haven't compared s13 bc's.
at my current height (around 37mm chassis) i have 5mm of travel before i bottom out.
also i have been quoted for just the rears, but it was $900
most of the changes aren't things that would be effected on a cert plate. plus you'll get further with a plate than not so its 100% worth having one even if you are outside specs, easy to revert back to cert specs etc.
Survived nats(just), almost ripped the gearbox crossmember off on the way home. https://instagram.com/p/0OklNeDdWN/?taken-by=cheesy_61
fixed that and have since done fuckall.
those shocks are pretty large, just a warning you might not be captive. not that itll matter at the track.
ae831's are the perfect length for me, 473mm extended as opposed to ae881s 553mm extended