Does anyone know the gradient profile of the WR, specifically either side of Bedale?
On the Leeming side the line must rise maybe a hundred feet between Bedale crossing and the level crossing between Aiskew and the A1 - basically the same rise as Aiskew bank on the road as the road is pretty much flat from the top of the bank along to the crossing
On the Leyburn side I suspect its not as steep, but must begin to rise from the new bypass bridge?
You have a very mistaken perception of what is 100 feet of altitude.
Bedale and Aiskew level crossings are about a mile apart, a mile being 5280 feet. An altitude change of 100 feet in about 1 mile is a gradient of 1 in 53. The only preserved railway gradient steeper than 1 in 53 that I can immediately think of is the North York Moors between Grosmont and Goathland, which is 1 in 49. It would be steeper that the 1 in 60 climb to Medstead on the Watercress line.
I have been to the Wensleydale Railway, though it is a while ago now, and have stayed in Aiskew, including doing the bus from Northallerton, so I know the road and the railway. I can also read the Ordnance Survey map. This shows that the Bedale and Aiskew level crossings are both close to the 40 metre contour line, and the railway follows close to the contour line between the crossings. The line is close to level track between the two crossings, with no significant gradients.
The road is different: from Bedale it climbs quite steeply up above the 50 metre contour, so a height difference of a bit more than 10 metres (maybe 35-40 feet), but there is then a more gentle gradient down the other side, so that the altitude of the road is back down to about 40 metres at the Aiskew crossing.