Is there any reference for that date for that kit , as I couldn't find anything .
I have never seen a manual, or any other document, if that's what you mean, and the only Admiralty Fleet Order I have with "tool schedules" oddly only includes Wright, PWA, and several special components (e.g., Holley, Chandler, Scintilla, etc), no Merlin, probably because it's strictly covering US aircraft and equipment, not US equipment installed in British aircraft (such as the complex Packard/Rolls-Royce/RAF/Merlin case). But, in addition to this most salient point...
All the tools are war era by date code and other tells.
...I would add the fact that I don't believe Packard was continuing to provide engines to Rolls-Royce for Merlins or any other applications that would require a kit with a logistics nomenclature (AT-xxxx) associated with the USAAF. The engines were of course wildly popular and snagged out of surplus with everyone looking to soup up their planes for Bendix, Cleveland, and Thompson trophy races, and many are still being used today, but I am not aware of Packard production, let alone toolkit production, in the 50's. I could be wrong.