You can scroll down on the 1099-R worksheet to enter his Basis in the IRA.

My concern is you said receipts for Basis in the investment.  That is different than Basis in the IRA.

I looked up code K and it almost seems to be an audit-me code.  🤣   My impression of code "K" means it is probably a self-directed IRA and they don't really know what should be in Box 1 or 2 so they just guessed.  😂