Taylor trunk for a cord circuit test set??

Picked this up on eBay as decor for steampunk art shows thinking it was your basic travel trunk, but closer inspection of the labels has me scratching my head. One riveted metal label says:

STEP BY STEP D S "A" BOARD
CORD CIRCUIT TEST SET
ITE-2286
SERIAL 014941

A paper label on the inside of the false top repeats this along with what looks like "EQUIPMENT SHIPPED LEASE" and a brief table of some electrical specifications. The top of the lid has very faded stenciled red lettering of which I can only make out the word "APPARATUS".

Googling these terms hasn't resulted in any direct hits for me, but it does seem suggestive of perhaps an early telephone switchboard circuit test kit, nowadays what a utility worker would have in a small box slung over their shoulder instead of this massive thing. The DS may stand for Directory Service.

Questions:
Anybody know for sure what this is?
When it dates from?
Any suggestions for restoration besides gently cleaning it (the thing is filthy)?