I remember that the -300 had a small L shaped angle riveted externally fore/aft at the point where the fuselage would strike the runway, this was to aid inspection, if the angle wasn't there then a strike had occurred.
I repaired a JEA -300 at Exeter, very straight forward, the damaged area trimmed up and a large preformed chemi eitched skin rivetted over the hole. The repair skins were on the shelf in stores ready for issue.
Nice picture of ZJ, this was the first Herald to be painted in the new colour scheme, when it arrived at Blackpool the general opinion was that it looked like a fag packet.