There's a kinder way to grip the splined end of the crankshaft than using stillsons.
Rather, use an adjustable spanner (10", 12",15" whatever tickles your fancy); open the jaws until they slide across the spline. They will grip the spline well enough to rotate the crankshaft, without damage or marks.
A gold star (mark only!) to the first forum member to dash off to the man cave and try it.
Richard