That would be the mighty 300K. There were also non-letter 300 models in 1964.

 

I was meaning like A body B body, C body designation. Thanks

 

I'm not sure it really had a designation. C body started in 1965 and it's not a B body.

 

This guy goes back before 1965, not sure he is 100% correct but it makes sense.

Especially as A is documented from 1960 and and B from 1962, possibly D from 1957.

Thinking about FWD vehicles the L was introduced before the G, H, J, K etc.

It could be a back dated designation like "Hemi," Chrysler didn't use that term until about 1965.

Thanks
Randy

Bodies: Chrysler RWD Body Codes - 1957-1989 (at http://www.dippy.org/forum2/index.php?topic=109.0 )

 

If you want to verify, 1955 (original 300) had no letter. 1956 was a "B", etc., etc.

 

In the first INF pages of the 1964 passenger car parts catalog, the model designations are broken down and explained:
http://www.earlycuda.org/docs/parts/64_Mopar_Parts_Catalog.pdf
The 300 is a 'C' body, more specifically a 'C2'. The regular 300 was a M (medium price class) while the 300K was a P (premium price class).
I have to believe that this catalog information is accurate.
I also recommend this book for historic 300 enthusiasts:

 

Then in 2005 we re-used the 300C instead of going to 300n.
I know that the m in the 300m was always lower case, although the earlier 300 letter cars were Capital letters.
The 1955 was also referred to as the C-300:
1955 Chrysler C-300 History by Dan Jedlicka (at http://www.danjedlicka.com/classic_cars/1955_chrysler_c_300.html )
The non-letter 300 may have stole some thunder form the letter-series 300. It was likely a marketing initiative.
The regular 300 was positioned between the Newport and New Yorker price class with the unique 300 grille and tailamps.

 

Perhaps the small "m" reflected the V6 instead of a V8. Not a slug at all though.

 

Thanks for all the replies and help, I know a lot more today than I did yesterday!