So I’m happy to say that there is a compatible fruit variety and a plum interstem that should work for peaches, apricots, and others!
I’ve got a Prunus Serotina with 1 out of 17 species and varieties that survived: Mirabelle plum!
Mirabelle plum (a myrobalan cross), is obviously a very useful interstem as well and this could be used for grafting almost anything on to Timber Black Cherry!