Chevy Master Cylinder Julian dates how to read?

[RALLY]

Guys 72 Chevy Nova is own. Master cyl cast numbers read 5470409 D53 351
Numbers stamped on flat part of casting where the first brake line exits and these read
3 2 0 4 CL.

Can you help me out here and tell me what these numbers stamped mean?
Casting number i believe is 5470409 D53 351- these are julian numbers 351 days of the year
reading Dec 17th? Am i correct?

Now i dont have any idea what these numbers stamped are 3 2 0 4 CL? Any input is greatly appreciated.