I’ve gotten seed from an old Danish landrace called “Grøn køkkengræskar” (Green kitchen squash). Traditionally used as a pickling squash. It gets pretty large and the fruits are varied, but mostly green with stripes. I believe it is a Cucurbita pepo.
I wonder which group to grow these together with. Do any of you grow squash for pickling? The fruits look a bit like those you call marrow, but I believe they’re eaten fresh.
a while back I ate some delicious sushi with squash known as Nikanpyo. Not sure if this counts as pickling but maybe it’s still of interest:
Is is a traditional Japanese recipe apparently using Lagenaria siceraria var. hispida a Calabesh/Bottle Gourd
The gourd is first cut into strips and dried, then marinated/cooked with Water, Soy sauce, Mirin, Sugar and Sake.
I have tried to recreate it using Hokkaido (C. maxima) and letting them sit in the brine for a while. It was good but not as good as the one I first ate.
I definitely want to give this another try, maybe with water bathing the result and make it shelf stable or even trying to find some of the originally used Gourds.
Never heard of pickling squash! So it’s harvested as a summer squash?
For my Hokkaido trial i used a mature one. Can’t really remember if i dried it beforehand. I think I will give it another go this year and can give you an update then 
