Upgraded with drawers and knobs several years ago and finally got around to adding the legs on the Kallax! The legs weren't as long as I'd wanted, but I was just ready
KALLAX Shelving unit with 4 inserts, white, 77x147 cm - IKEA
Ikea, KALLAX Insert with Drawers, Furniture & Home Living, Furniture, Shelves, Cabinets & Racks on Carousell
IKEA KALLAX Insert with 2 drawers assembly instructions - YouTube