Based on those changes, I’d be okay with a 55hp bump and a 75hp - 80hp bump in Valk.
The cast time idea is cool. I was also thinking of her cast time being affected by how much health she personally has, rather than her team mates (I.e. a low health Mercy will take longer to rez than a higher health one.)
Also, her rezzes being given every 30 seconds is a bit too much in my opinion. I’d prefer her to be granted individual Rez charges as well so she earns them, rather than just having them handed out to her. 2 to start with, that are unlocked after a certain threshold of healing is reached, and an additional one granted when she ults. OR. Just give her 3 charges and make it exclusive to the ultimate altogether.
If rez is tied to her ult, she would also have space open for another ability. I’m not too picky with what, but I’d like to see some skill-based ability that prevents death proactively. I’ve suggested something called “Halo” in the past that shows kind of what I’m talking about, but there are many other ideas proposed as well besides this one.
Just some ideas on what I’d like to see. Though there has been many other great ideas as well. 
~Sincerely Yours xoxo,
a Lover of True, Fair, and Fun Balance.
xavvypls 