A GlobalWin FDP32 or the Golden Orb should work. If your processor is made within the last year, you may have a chance to take it up to 500MHz. But if it was one of those first K6-2 400 that came out in late 98/early 99 then you should forget about getting a better heatsink and overclocking it.
Also a bit more info, my last K6-2 450 made it to 560MHz (5x112) @ 2.6V on a FIC VA-503+
Tony