If you are interested in a long block that is already rebuilt, have a look at sandjengines.com. They are in Spokane, WA. Their website lists a rebuilt 5 bolt 289 long block. Part # FO-289P-2. You could call and ask about overbore. I have no affiliation with the company. Prices seem extremely reasonable, supposedly in business for 35 years, seven year-70,000 mile warranty, etc. I bought a 6 bolt from them earlier this year (.030 overbore), then got busy with other things and have not yet installed it. Suddenly the old 260 started to run a whole lot better with a faster advance in the distributor and a rebuild, bigger squirter and different powervalve cam in the Holley 4 barrel carb!
Cheers, Gene