I am a mechanical fan but elk is where my fandom stops. I shoot a low 90s KE setup and have cleanly taken bull elk with mechanicals. I however have seen elk rib direct hits significantly lower penetration. They got the second lung but not by a lot. I have to believe moose ribs would reduce penetration even more on a direct rib hit so wouldn't chance it.
I would be shooting a very sharp and durable fixed for moose. I have only harvested one moose so don't have a ton of experience- take it for what it's worth.