Peter,
XK140 had A type head, or XK140MC (in American terminology) had optional C type head.
B type head not available until XK150, Mark VIII and 3.4 litre (Mark 1)
The item for sale came from a straight port cylinder head, it will not fit on a B type head.
Cylinder head engine number stamping would have started with VAS.
V=XK150
A=3.8
S=triple 2inch SU’s.