Congrats Pete on saving a heritage apple tree. Many new apple varieties are grafted onto a hearty root stalk. In your case I suspect the old apple variety is growing on it's own root system so all you need to do is root a cutting. The basic steps are below. For more details you should consult a propagation guide or contact your local extension service about rooting cuttings in your climate. The best tip I can offer is to take many cuttings at different times of year with different growing mediums and eventually one will "take" or form roots

1. Cut a shoot from the tree that is the thickness and length of a pencil. Make sure there are nodes or growth buds on the cutting.
2. Inserert the cut end into a clay pot filled with damp sand.
3. Cover top of pot with clear plastic bag to keep humidity around the cutting. Vent the plastic if moisture forms drops on inside to prevent rotting of the cutting.
4. Be patient. In 4 to 6 weeks roots should form. Then pot up cutting into a mix of half sand and half potting soil as more roots form. In a year the cutting may have enough of a root system to grow outdoors in the soil.
5.      Good Luck and Keep Growing, Marianne Binetti