M27 is an apple but the fruit probably isn't edible. The best technique now is T budding. All you need is a sharp knife and a couple of large rubber bands. Utube should have plenty of videos on the subject.

Thanks fruitnut. Have you ever heard of using hawthorn as a rootstock?

Any top stock that you would graft to a hawthorn has to be a member of the hawthorn family, whatever that is.

Not necessarily,barkdust.

Some pears will work on hawthorn understock; I've got at least one that's close to 15 years old now, grafted on native C.crus-galli understock. Suspect that quince(Cydonia) would probably work, and possibly medlar, as well.
Some nurseries offer named selections of Amelanchier x grandiflora on hawthorn understock.

Also, I have several mayhaw selections grafted, growing, and fruiting on the native cockspur hawthorn - but, as barkdust suggested, they are in the same genus, Crataegus.