Sheaffer Balance sections and feeds

[FredRydr]

Can anyone refer me to a comparative illustrated study of the evolution of Sheaffer Balance section and feed attributes? Online or printed, perhaps it might be part of an article about the balance of the pens (pun intended).

For example, you can see two different styles of sections in the four oversize lever Balances in the photo (below). What's more complicated are the feeds. There are four different styles showing in the photo, but another hidden variation includes external or internal ink channels.

Thanks in advance!

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