It hasn't been active in a while, but one of the Sun collectors on the Sun thread might know more about dating it. You can find the Sun thread in the A-Z Index of threads in the Sticky at the top of the forum.
When the testers changed into the 60's design, these cabinets appeared on the scene. This might have happened in the late 50's already, but that cabinet is clearly the 60's design.
Here we have the cabinet of the 40's and 50's. In the 40's the testers were coloured blue, changing into red with the following decade.
Then, with the sixties, the design of the tester itself changed as well as the cabinets. First the smaller units, like the 200 series single purpose testers and large testers as the 900.
The seventies brought a growth in size. The units and their gauges then were delivered almost as double large than before. Suitable for seniors, if you allow that joke. The cabinets remained the same, test units were the 1020, and later the 1130.
Followed up by the 1010, now sitting on a slim shelf.