Hi there Wow how lucky ru??
I would love to have wild plums in my back yard.. We have had our lotty now for around 7 mnths and just planted a lil Victoria plum tree and she is growing strong.. despite the harsh weather..
But we also know where to get hold of the wild plums that you speak of.. we collected about 35 lbs of them last August/Sep time
depend on how they are ripening. we made tones of jam and fruit in syrup and just ate them too.. You are right about there being 2 kinds of hips and as far as I know you can use both of them.. BUT I TEND TO STICK TO THE SMALLER ONES I made rose hip syrup for the 1st time last year and it was really good .
I will be doing it again this year too.. good luck with all you do..
Regards Potty