Yes and no; assuming the gun is original, the 45-90 was an express case meaning that it used a light bullet and lots of powder in the hope of getting a flatter trajectory. The most common factory load for 45-70 is a 400 grain bullet and I suspect that might be a bit heavy for the 45-90 to stabilize. If you can establish your rifles twist rate, you can calculate the heaviest (longest) projectile it can stabilize using the Greenhill formula of L = 150 x D squared over T. Work on the basis of needing a twist rate of 1" faster than the formula calculates. You can calculate the twist rate using a tight well oiled patch on a ramrod with either an easily pivoting handle or a delicate hand allowing the rod to turn with the rifling. Put a piece of tape on the handle end of the rod to act as a flag to show you a full turn or half turn etc.
cheers mooncoon