This package contains picture of An Alternate Universe where the Prismriver-sisters are alive and kicking, some drawings and useless trivia behind the story of "The Prismrivers". pixiv #40811235»
Not totally sure I get this one... I figured out the tractor is an actual mid-20th century Finnish model (a Valmet 20), but beyond that I'm kinda lost.
Yeah, that's probably all it is. I guess I was looking for some sort of hidden joke, like if the tractor had a Merlin-supplied motor or something (cf. post #1653505, panel 2).
I don't think there's a joke to it. It's just the sisters with a Finnish tractor.
Pikku-jehu wasn't made until some years after the war, so maybe it's another "if they lived" thing.
The other rather common nickname (which I personally prefer) for this tractor is Piikkilangankiristäjä, I suppose it could be translated as barbed wire tightener.