I would doubt it would come back via North Cornwall Railway (NCR).
Light West Country/Battle of Britain Pacifics were allowed on the NCR but once rebuilt were banned as too heavy. In fact, in rebuilt form, they were only allowed over Meldon Viaduct after it was strengthened in Summer 1961 I believe.
Of course it would have to travel back by rail in any case. Often when heavier trains than normal travel over a line a speed restriction is imposed on them. I would suspect that maybe the loco travelled 'light engine' with a restriction of 5mph over the RAB.
Perhaps someone with more knowledge, or a member of the Cornwall Railway Society would have more information for us?
I expect returned to Devon over the bridge again. If it went back via Bodmin General and Wadenridge, it could have taken the
GWR▸ branch at Launceston to Lydford and then picked up the Southern Main Line through Tavistock back to Plymouth, thus avoiding Meldon.