Planting squash and pumpkins on a slope.

Hmm that's interesting, you would not want a 26 stone pumpkin rolling down the hill at you 

That's a very steep slope but I am sure they would support themselves or you could put some stakes either side of any pumpkins and some netting to support them.

Thank you, I'll give it a go.

and maybe cantilever a small shelf.....

From what I've heard, pumpkin stems are surprisingly strong and they'll happily hang in mid air without any help.

I'm not sure if that applies to Atlantic Giant and the like...