The "Steamship Round" is basically the whole primal Round (Top Round, Bottom Round and Eye Round) with the shankmeat removed from the bone and the Sirloin Tip removed. But, that depends on the packer also. It can weigh up to 50-60 lbs, sometimes smaller, depending on the size of the cow.
It's great for 'display' purposes and putting on a show for large groups. It is best slow cooked on a spit, unless you have a large commercial oven available. Most chefs will sit the cooked roast standing up (bone in the air) and slice the meat thin. The tricky part here is that the grain will run in different directions, keeping the carver on his toes. Sliced thin against the grain, the meat will be relatively tender.