import cadquery as cq
w0=cq.Workplane('YZ',origin=(40,0,0))
r=w0.workplane(offset=-81/2).moveTo(-35,30).box(130,106,81).union(w0.sketch().push([(58,-16)]).rect(84,134).push([(58,-15.5)]).rect(18,21,mode='s').finalize().extrude(-35))