the boots in that location is the place they are been looking there

I just finished this quest line, got the entire armor set, worn, and finished the quest line in the hall of echoes. Everything upgraded to level 20 except the gloves.

Where do you find the chest piece?

can I get all the set if I missed the Devourers Claws and book on fort Joy? (i missed the quest acquiring basically)

for some reason the gloves never got the "devourer's slumber" bit attached to it nor did it lv up to level 20 (did it myself manually with diamond dust), now even when wearing the full set it gives no benefits.

When going for the books in orrivands chamber it reveals that the boots are in the house not the gravediggers body

To get the chest you need to go to Kemm's gardens and unlock the hatch by finding the hidden lever by the hand water pump by the waypoint. Once inside you need to deal with the patrols one way or another then head left and go through a hidden door. Once inside, there will be a cabinet with 3 buttons. The order is 2 3 2 1 1 3. It will appear inside the cabinet.

For me you needed to get the helm first then the chest because the spirits wouldn't appear until I got it.

A question about the Devourer armor healing ability. If you are an undead, do you take damage instead?