f116v is a decryption attempt?

[oshfdk]

I wonder if people have ever used for real lengths of things etc to encrypt hidden messages within innocent or misleading ones?  Like, the number of letters in each line, modulo 26, is one letter of the message?  Or the length N of the paper in 1/16ths of an inch is an index into a codebook?  Does Trithemius and his gang mention this possibility?

Yes, as far as I remember. There were hundreds of different schemes that could use unary, mainly to encode messages in images. Most of them were optimized to use binary * (two counts to encode the character position in a 2d table), but in principle would work with unary, that just would be very cumbersome. For example, there was a scheme that used the count of leaves and flowers in plant images, with branches used to separate characters. Like, two leaves and one flower on the first branch, then 5 leaves and no flowers on the second, then 3 leaves and 3 flowers on the third - three characters encoded. It was impossible to encode large texts this way, but 1-2 words per image was possible. I think it was not used for communication, but to state hidden identities or as easter eggs - encoding names and mottos.

*edit
I don't think this can be called binary, binary is positional, while this encoding essentially is more like compressed unary. So, with item V corresponding to 5 and item I to 1, 22 (as 22nd letter of alphabet) can be encoded as VVVVII or VIVIVV or VVIIVV. Or maybe even VIIVIIIVII. Given that the Roman numerals are made in a similar way with additional restrictions, this encoding would be obvious for most people of the time.