If you are going to make sub 650rwhp (Which the KB will) and you don't plan on tracking the car twice a week it will last quite awhile IMO. That being said, a solid tune, frequent fluid checks/changes, and a bit of common sense in terms of how hard you drive the car how often will certainly extend things quite a bit.
For example, we have a client's Procharged + Cam + Headers SS that made over 650rwhp more than a year ago. He drives the car HARD. Tracks it often. Broke the Tranny. Broke the driveshaft. Broke the Diff. Ran it on slicks/skinny's and DR's on the street. I watched him hot-lap it on a private rental day like he was TRYING to break something lol.
To this day the engine is bone-stock and with Meth and twin-pump fuel system it made almost 700rwhp. I wouldn't expect this to happen every single time but it is working for him
Jeff