if the tube spaces isnt long enough, you just have to put an extra thin spacer or two between the bearings with it. its a bit fiddly, you can either tape it to the tube spacer or put one bearing into the frame, put your crank axle a little way into the bb, then put the spacer and tube on, then put the second bearing in.
you can get away with not running the tube if you have powerbites or other pinchbolt cranks, but you probably should if you can