Steadies lead the tool so since most turning is done right to left they are normally to the left of the tool.
Think its a harrison one. I have or had one that looked exactly like that for my original L5, I'll have a looksee and take a snap and measure if that helps if I still have it. The later one has a different arrangement though as it bolts the side of the cross slide instead of clamping on the ways as the cross slide has a rigid cover on the later ones.It may well be a travelling steady but not for a boxford