Lets face it, Ancient plate set is a total bust, short of going toe to toe with trojans (and maybe a few other monsters) you never see it used in T3 (where most 5star armors are used), plus you don't get a good return for those ASI and MSI debuffs. Short of being paired with ASI UVed weapons and BKC in LD few people use it at all in the clockworks.
Lets make this armor set a worthwhile pursuit for the player by giving each piece a shadow defense bar (comparable to the elemental or pierce defense of the other 5 star plate armors). In addition let's give it a Curse Resist (considering its rarity ingame this isn't a huge buff but it provides a new status).
The HP boost this armor gives is pretty much negated and more by the current defense type and the debuffs, providing it with another defensive type and a status would truly make this a boss armor set to get.