No return spring as such , but there is an over center spring that should be there but is often removed , it aids in both depressing the pedal & bringing the pedal back to the top [OK I can see the picture now , yours has been removed ] , it sits over a button on the pedal , this is often removed if a diaphragm type clutch is used . There is a spring on the z bar to the belhousing though , the clutch pressure plate pushes back & raises the pedal most of the way up & the overcenter spring pulls the pedal away from the release brg .
Personally I do not use diaphragm style clutches in these cars as the linkage is not designed to work with them , the pedal feel is wrong & at Higher RPM the pedal can stay on the floor & not return , best to have a rev limiter if you use a diaphragm !!