Hello Eric
As there have been some doubts raised I am sure you are right to withdraw your frame from sale to give you time to investigate further. You may find it useful to compare your frame with a Merlin machine currently for sale on ebayUK , No 270319751498, which I think by the style and the lugs used is more likely to be mid 60s to mid 70s. I currently have in my possession three pre 1954 JRJs and a Merlin, and none of them bear any resemblance to the ebay Merlin. One of the common features of them all is that they have a three figure frame number stamped upside down on the top portion of the right hand dropout, but that practice may have ceased in later years, and certainly the numbers would have become four digit by mid 50s if they continued the same numbering sequence.
Good luck with your research.
Regards Peter Brown, Lincolnshire, England