I think Griselbrand is fine in the context of the top end of your power band if you want to play it, but I do think you would need to make some modifications elsewhere to balance it out.
Archon of Cruelty is obviously good so you don't need to change that if it's causing no issues. The same is largely true for
Myr Battlesphere with the added bonus of it being a tinker target. Meanwhile,
Phyrexian Fleshgorger is a worse reanimate target, but it has actual value in fair midrange decks and also combos with blink stuff.
However, I think these two cards are bad if you want to play powerful threats:
Thorn Mammoth is fine but it's closer to an overgrown
Affectionate Indrik than
Craterhoof Behemoth or even
Woodfall Primus.
Anegel of Serenity is like...
fine, but you can do better
. It's definitely not the most exciting reanimation target, even in White (that is probably
Serra's Emissary,
Avacyn, or
Elesh Norn). I think if you want to be running the four aforementioned cards, I would definitely suggest cutting these because they just do not line up well as options. For
Anegel of Serenity, I'd go with one of the aforementioned White cards or maybe
Ancient Gold Dragon if you're feeling like playing a spicy weaker card, and for Thorn Mammoth I would suggest playing
Apex Altisaur which is basically Thorn Mammoth but significantly cooler.
I would also consider adding some more interaction. I don't really have any problems with reanimator in my Modern-ish power level Cube, but that's because it's easy to answer the threats most of the time, thanks to my removal density. In your Cube, I would worry about the reanimator decks being un-fun to play against because there isn't quite enough removal to effectively dispatch the threats. It seems impossibly difficult to beat a turn 2
Reanimate, even on one of the less potent targets like
Phyrexian Fleshgorger.