An ATI damper can't slip because the outside is directly attached to the crank hub, right? The o-rings & weight inside are what move.
A must in any motor build (in my opinion)is to put a piston stop over #1 piston & check for actual TDC with the heads off & timing cover & pointer installed. Lots easier than later having to remove the #1 pushrods & put a piston stop thru the spark plug hole. I always do this with only the #1 piston in the motor (lots easier to turn), then remove the timing cover & degree the cam. Then I install the remaining 7 pistons & rods. Make sense?