I don't own Legends of the great western but from what I heard and seen you can't use the 52 on SEHS and ECW
You can use the 52 on SEHS if you do an Off The Rails scenario. However I could only do it in the Down direction, as for some reason St Pancras wasn’t selectable as a destination starting at the country end. Great fun running through the tunnels, no signals of course on the HS section but mine was the only train. Would be even better if the reverb was working and slightly lighter tunnels!