Early model B headlights mount with a bracket?

39 Bs were in a period of transition like the 38s.  If your 39 had no provision for mounting a generator bracket to the block it probably was a hand crank only B without any lights when new.  Radiator surround if it's vintage and original was not threaded for mounting headlamps. It is pretty hard to tell just by the serial number on the transmission what year all the parts an any givin  B tractor are.  Many Bs with 39 serial numbers could have been updated  with parts from later Bs with electrics.