The crankshaft will have to be measured to determine if you need stock or undersize (when concerning a crankshaft, undersize is used) bearings. It is likely damaged if there is a rod knock (along with the connecting rod).
Undersize bearings are meant to replace the stock size after a crankshaft grind is done, and they are usually -.001, -.010, or -.020.
If he is planning on just sanding and slapping a new set of bearings without removing and machining the crankshaft and rods, it will just be a band-aid at best. Could last a week, could last 6 months depending on the situation. To do it right, the engine should be disassembled, crankshaft measured and ground to bring it back into spec if needed, and the rod journals checked for out of round...and machined straight....which is a common occurence with a rod knock.