I don't know that safety is really an issue when canning plums as they are an acidic fruit - unless they are windfalls that are more low-acid. There are many recipes for Brandied Plums available but the standard Canning Plums

instructions should work fine as you would just make the canning syrup out of brandy and sugar rather than water and sugar.

Otherwise of the several previous discussions here about this I think you'll find this one the most helpful.

http://forums.gardenweb.com/discussions/1952336/preserving-plum-in-alcohol?n=2

Dave

Thanks again!