Yes, I would assume the MTB has 73mm(?) BB shell, but the fact that the old BB is marked 68/70 made me think it was probably a road size.
Yes, I should actually measure it... but it's bedtime, so I'm not going out to the garage now. Will do that in the morning.
And yes, there was indeed a spacer between the drive side cup and the frame.
I kind of know all this shit, but I was thrown a bit because Samox isn't a brand I'm familiar with, so I'm wondering if there are compatibility issues I need to be aware of (not least because I've had trouble mixing and matching Shimano and FSA components in the past).
I guess I should probably also measure the diameter of the crank spindle, though I am assuming it's 24mm.