If they are the same as the wild plums here, they make a pretty decent wine. I have only made it once and it is not finished yet. Froze them last summer and started the ferment in March. Kinda made this up as I went along but this is about what I did.
32 lb. wild plums. most stoned. used the cherry pitter to stone them. had to adjust it some, but worked pretty good.
Enough water to come out with about 6 gal.
K-meta or campden tabs 12 hours or so later Pectic enzime.
Added bentonite
I put some tannin in, in the amount it was recomended on the bottle.
yeast energizer
yeast nutrient
Sugar to 1.090
Used champaine yeast, basement was cold so it was a slow ferment.
When below 1.000 racked to carboys.
After the gross lees fell out, racked again, added k-meta and it is still sitting.
at this time, it is not clearing very well. Will let it sit for another month or so, maybe two or three and hit it with sparkaloid.
Sometime this fall or winter, maybe next spring will bottle it. It will have to be sweetened a bit also, at least for me.
Good luck with it, Arne.