I feel like this isn't quite right, but I'm guessing it's
Take me finally with you
An autopsy is the last ("finally") thing to be done to a body before the burial or cremation process begins.
to label your pain
To determine the cause of death.
for who wants much without me
wants it in vain
Here's where I start to lose confidence in my answer. Maybe because trying to know the cause of death without the autopsy is (generally) an effort made in vain?
Inquisitors of Spain
mark my words and be led
wander by my wonders
as I stand on my head
I... don't know. It's late and I shouldn't even be awake.
So curl your last scratches
let me raise your voice too
Give the deceased a "voice" by revealing the cause of death(?)
for journeying here without me
"Journeying here" to the afterlife, i.e., dying.
makes most give up on you
No autopsy generally means no definitively known cause of death, so in essence we "give up" on knowing what happened.