You might set the dampener slit at 15 ATDC then with a 1&1/4" socket/breaker bar bump it back CCW carefully till the slit JUST centers on the TDC mark. have a helper watch the rotor and you bump the breaker bar back CW carefully till he hollers that the rotor JUST moved & that'll tell you how much timing change (spark scatter) you will be dealing with which is chain slop and dist tang slot slop combined and subtract the # of degrees of slop in the intergear/dist tang interface for the actual cam phasing change (yes, retarded). Twist the rotor lightly just not enough to get into the springs & measure the circumferential distance/play plus some math (c=PixD) to get the amt of intergear/dist tang slop. As said all chains stretch & a high dollar one (Rollmaster) will minimize that on a high dollar/racing app (as needed). EDIT on the intergear play multiply that by 2 to get the crank phasing number