Were the "correct needles on e-bay" these: http://tinyurl.com/ltq8u7
("Linkert M53, M53A1, MR3 , MR4, MR4A High Spd Needle", advertised as "This is the CORRECT needle ( copied from an original NOS item ) for the M53,M53A1,MR3,MR4,MR4A carbs, straight venturi or bombsight versions, high speed side. Also used in various racing versions.")?
The 27297-52 replica they're selling is evidently not the same as the MR-4 27300-46R, used 1946 until at least 1954 - why would the factory change it, since the M53 was already in use?
But you already knew that...