Coming to this a bit late ....
There's an article in the Dundee Evening Telegraph of 22 April 1938 about the body of William Munro being found on the railway line near Benarty Bridge. This death was registered in Cleish.
At this time deaths had to be registered in the district where they occurred. Therefore Benarty Bridge must be in or on the boundary of the parish of Cleish.
The article also says that the body was found by the driver of a coach going from Kinross to Cowdenbeath.
Rumbling Bridge is several miles further west, between the parishes of Fossoway and Muckhart, and it spans a river, not a railway, so it can be ruled out. Auchmuirbridge is also a bridge over a river, and is several miles east, on the boundary of the parish of Portmoak and the parish of Leslie in Fife. So it too can be eliminated.
Trains from Inverness to London these days mostly go from Perth via Stirling. There is still a line from Perth through Fife, but it goes miles east of Kinross, Cleish and Loch Leven, and carries mostly local trains. The Aberdeen to London main line goes through Cupar, Markinch and Kirkcaldy, still further away from Cleish.
The only railway line anywhere near Cleish was the Perth and Inverkeithing Section of the North British Railway, which branched off at Bridge of Earn and went through Glen Farg, Milnathort, Kinross and Kelty to rejoin another line at Cowdenbeath. This line ran for about two miles through the eastern end of the parish of Cleish, skirting the west end of Benarty, the hill that rises south of Loch Leven. The North British Railway (NBR) became part of the London and North East Railway (LNER) in 1923.
So Benarty Bridge has to be somewhere between Gairneybank and Keltybridge, and close enough to the road for the driver of the coach to see the body on the line. This further limits the possibilities, because there's only a short stretch where the railway and road were that close to one another - between Blackknowes and Lochran.
See
https://maps.nls.uk/geo/explore/#zoom=15&lat=56.1655&lon=-3.3979&layers=168&b=1and
https://maps.nls.uk/geo/explore/#zoom=14&lat=56.1624&lon=-3.3999&layers=8&b=1There were two bridges over the railway in this short stretch, one at Blackknowes and one at Lochran. Between these two bridges was Blairadam Station.
The coach driver reported the find at Kelty Station, which suggests that he did not see it until after he had passed Blairadam Station, so the body must have been somewhere far enough south of Blairadam Station for it to be described as 'near Benarty Bridge' rather than 'near Blairadam Station'. Though further investigation reveals that Blairadam Station was closed for passenger traffic in 1930, so maybe there wasn't any way of reporting it there, in which case it could be further north. See
http://www.geograph.org.uk/photo/1828403Therefore I reckon that Benarty Bridge must have been the one just east of Lochran, at the south end of the stretch where the road and railway ran close to one another. It's also the closest railway bridge on the direct road from Kinross to Cowdenbeath and in the parish of Cleish to Benarty House and Benarty Colliery, both of which are south of Benarty Hill.
Does this make sense?