[Hallicrafters] S-53 questions

[Jim Jones]

Let's try again.I have 2 S-53As.  The first has an all dark gray cabinet and has no serial number. The chassis no. is 199542 Run 2A.  
The second one has lower cabinet dark gray with the lid light gray. Serial no. is 180061, chassis no. 199731 Mark 2A. The first has silver disk in the tuning knobs while the second has all black knobs. Can anyone tell me date of manufacture of these sets? 
Can anyone tell me the significant of the chassis numbers?
The first is the one that has the incorrect dial glass that I asked about a while back. I hope to remove the good dial glass and make a duplicate some way for the other radio.
Thanks for any help.

Jim, NG9E