I believe your choice for Elk in heavy timber is a good one, provided proper bullets are used. I've only used a 45/70 on game once.

When I first started hunting, before I owned any rifle of my own, I borrowed a 45/70 that belonged to the father of a friend, and a box of factory ammo. All I remember about it, is that it was a lever action, had a 4X scope on it, and after shooting the M16 in the service, thought that it was the most powerful weapon in the world. To my inexperienced mind, it really kicked like a mule. With it, I got really lucky, and shot a 185 pound dressed, male Black Bear here in Pennsylvania. I shot it in heavy timber surrounding a swamp. The shot was around 45 - 50 yards, and he ran about 100 yards after being shot through the lungs. That was the first big game animal I ever shot here in the US.