The GR60 has a nice tremelo but no reverb. The GR60 also has different output connections and an output power switch. I think these differences date this amp to the late 1960s.
This second GR60 was acquired in March 2019. I’ve shown some before, after, and internal pictures. The “after” pics show that I’ve replaced the original Bulgin power and speaker connections with IEC and Jack sockets –