The website Paper Sizes provides a wealth of information about paper sizes ancient and modern. As they say, before we were blessed with international standards in this area, we used a charmingly antique vocabulary to talk about paper sizes. Before paper making was industrialized, the sizes were determined by the size of the mould and the deckle, and this in turn was limited by the length of the human arm.
First, Uncut Drawing Paper Sizes:
Then Uncut Printing Paper Sizes:
For more in this vein, please see Demy octavo, and Paper sizes.
Making Book 
I have long yearned for the opportunity to use “foolscap” without sounding unbearably pretentious. Alas, I may have to suck it up and go all in with the pretentiousness.
When I was at school foolscap was the paper we used. I’ve often been told to take out my foolscap pad. Alas no more: it’s all A4 and A5, etc.
So you’ve clearly got to write about old-time British school children. Maybe a bit of cricket could be worked in to your baseball history!
If you try to write about early baseball without working a bit of cricket it, you aren’t doing it right.
So all you need now is an interruption to the game where they have to go back to the classroom to do a test on their foolscap pads.
. . . or even slicker, you could refer to cricketers keeping score on a ruled-up foolscap sheet of paper — as they probably really would have, as I bet the preprinted sheets used now weren’t available in the nineteenth century.