the high revving and light 4ag is heart and soul of an ae86
putting a mundane ka into it just for more torque and hp is something you don't want to do... not to mention the extra strain on the chasis do to the added power... ur gona have to do ALOT of chasis/drivetrain reinforcement to make it work....
also the amount of work ur gona have to do to make it work is not gona be worth the cost and end product
ur prob better off spending that money and building up your 4ag 16v...
then again I've heard 4AG-ZE's going for 800... that makes more power than ur KA
also a 4AG-ZE is a straight drop in comparison to what you're trying to attempt with the KA