I could be wrong but this listing on fleabay sure looks like a loading tool box for the top of the battery box on a Mk1 carrier.
https://www.ebay.com/itm/WW1-RUSTON-...Ceu:rk:22:pf:0
They list it as a WW1 engine bolts box, but it sure looks like the box I think it it. If it is, I'm sure it will make some MLU carrier owner very happy to find an original.