Apple pear / asian pear in most cases should be one in the same. They graft to pears normally. There are exceptions.
There is a interspecific hybrid called an apple pear grown on apple rootstock. @39thparallel grows it. Very large green fruit that ripens in late summer/ early fall. Mike can likely tell you more about the apple/pear than nearly anyone. They are good tasting fruit.
Was your grandpa a grafter?
We will gladly help you get started with this. Do you know where the tree came from?
The apple pear interspecific hybrid if thats what it is may have originally came from Richard Fahey who can only be contacted via mail. It may have originally been from ars/grin. To contact Richard send a SASE for his scions list. He might respond to questions if you send a sase. The address is Singing Tree Acres Rd 2, Oxford, NY 13830. Richard is in his 70’s+ so he does not use things such as email or internet.