Bottom Bracket length for Kooka Cranks

[yagamuffin]

After more advice! Does anyone know what length bottom bracket I should use for these Kooka cranks? I've checked a few of my usual places but am none the wiser.
If not, id there a way to calculate or should I just suck it and see?

Thanks

IMG_20200531_124305_767-ink by Phil T, on Flickr

 

[jimbog]

Did you ever find out? I’m trying to work this out too.