You did the right thing asking the K-1 preparer for details, if they weren't already provided.  The IRS instructions are, "Other property (code C). Include all distributions of property (other than money) not included on line 19a that aren't section 737 property. In figuring the amount of the distribution, use the adjusted basis of the property to the partnership immediately before the distribution, taking into account any adjustments under sections 732(d), 734(b), or 743(b), as applicable. In addition, attach a statement showing the adjusted basis and FMV of each property distributed."  If you can't get that, and your client doesn't know his assets from a hole in the ground, than make an educated guess based on other details from this and prior K-1s.