No one really knows what Donald’s Grave was. The OS maps, from the first edition in 1860 onwards, all show it at the position of the marked stone you mention. From the lettering on the stone, and its position, it seems fairly certain that it is a boundary stone for Bulbeck Common – there is a whole series of them (mostly listed monuments) probably erected when the common was enclosed in the 1770s. Of course they may have simply used a conveniently placed older stone marking Donalds Grave and carved the lettering into it.
