[Hallicrafters] S-53A

[Jim Jones]

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.
Another question.  What kind of tool is used to remove the smaller knobs of the radios?  I was able to remove the tuning knobs with an Allen wrench, but the other knobs seem to need a square wrench to release.
Thanks for any help.

Jim, NG9E
I talk to the world and drive Route 66 in my Miata.