Bill,
It sounds like the person that built the street rod may have used a 28-29' year frame and mounted the 31' body on it. The front cross members on the early and later frames are different. The early cross members have a raised boss where the radiator mounting bolts go (one each side) and the later 30-31' cross members have a lowered boss to mount the taller 30-31 radiator. Check that first and let us know. Mike