Had (eichen). Regular imperfect here, no longer echōn.
For a measure a golden reed (metron kalamon chrusoun). See Rev 11:1 for kalamos (reed). Metron is an old word, kin to mētēr (mother, moulder, manager), an instrument for measuring (metreō) as in Mat 7:2, here in the predicate accusative.
To measure (hina metrēsēi). Purpose clause with hina and the first aorist active subjunctive of metreō. The rod of gold was in keeping with the dignity of the service of God (Rev 1:12; Rev 5:8; Rev 8:3; Rev 9:13; Rev 15:7).