This is taken from Dorset Brrows by L.V.Grinsell and describes these long barrows/ bank barrow.
“Width includes probable berm ploughed to edge. Height of mound rises from NW to SE where 5ft. This and the last (II a) may in fact be one long barrow, as probing by R.J.C.Atkinson has shown ditches to be continuous.”
Grinsell gives the following dimensions for both barrows : IIa – 300 feet long by 72 feet wide by 4 feet high.
IIb – 175 feet long by 70 feet wide by 5 feet high.