They should change the locomotive if it's too big to be turned..it was a tight fit at St Blazey on the Royal Duchy.
For the latest run they took the Duchess off at Plymouth, to be turned & fueled at Laira presumably. Had there been significant problems on the previous run with turning?
In my longest engine suggestions above I'd omitted (ashamedly) the P2 which, at a shade over 64 feet, beats even the old A1/1.
Makes me think it might be worth the P2 rebuilders being able to offer an alternative shorter tender, interchangeable as required, perhaps also with Tornado, for greater flexibility and compatibility with the limited number of main line linked turning opportunities in the west and elsewhere. Otherwise such large locos might risk being limited to the wyes, at Norton Fitzwarren and Laira in the west, for example, or to circular tours like the Exeter round trip out via Southern, back by Western (not so common the other way round!) A shorter loco and tender combination might help getting more appearances on heritage railways too.