This may not fit your situation depending on what the 1245 assets are, but I've often used their sale price as their remaining basis. If you bought a water heater for $1k 10 years ago, its basis is zero--which is exactly what a willing buyer would be willing to pay for a 10-year-old water heater. Same with awnings, driveways, used furniture. Usually the amounts involved aren't that big so it doesn't over- or understate the total profit a heck of a lot. There is a form where the buyer and seller agree on the purchase price of each asset (8594?), but I have never seen one outside of tax classes. You can tell your client to take a stab at it and see if the buyer agrees to those numbers as those will be his/her basis going forward. (Warning: the seller will want low valuations to minimize profit whereas the buyer will want high valuations so there is something left to depreciate.)