the k3 had longer shocks, titanium screws and a milled chassis.
get a milled chassis from wherever, I like JT racing and Fioroni myself, take out 2 brake discs, change the centre LSD for a standard diff and you're practically there.
One recurring compaint about the K3 was that many people thought they paying more for less, as the main aim was to strip the K2 to make it lighter.