We had a problem understanding this rule 35 years ago and it was not until somebody..... if I recall correctly, it was JD Tone.... pointed out that IT IS NOT IN RELATION TO THE ORIGINAL POSITION OF THE ENGINE.... THE ORIGINAL POSITION OF THE ENGINE IS NOT RELEVANT.... it is only from the criteria included in the book.... if you have a 100" wheelbase car, the setback is a maximum of 2" BEHIND the front axle centerline.... being that we were allowed a 2" body stretch (similar to NHRA pro stock rules and which put us into Altered-where 25% setback was allowed)... it all went out the window for us anyway... but boy do I remember the snail mail exchange!!!!! and you would think that, after all these years, (and NHRA having similar rules too) that the definition of setback would have been made clearer....