[GreenKeys] Teletype configurations

[Nick England]

I still have a lot of learning to do and you guys have got the answers
so here goes...
How do you find out what components go with a particular Teletype model number?
For example, I'm looking at Bulletin 1167B covering Typing Reperf
parts. There is a chart that tells me that this book covers parts for
18 different models of the Base LRB2, LRB3,...,LRB32 etc. And the
parts pages show single plate and double plate and multiple reperf
bases, but how do I find out what an LRB21 actually has in it?
There's bound to be some publication that has the secret codes, but I
ain't found it yet.
Please point me in the right direction, oh wise ones.
signed,
Grasshopper