Tranny mount bolt hole locations

Most 510's have the nuts for the tranny mount bolts located here as shown: Frome the seat rail, about 10 1/4" to the rear nut and 12 3/4" to the front nut. Some shells (mostly 71 automatics) have the rear nut at 12 3/4" and the front nut at 15 1/4". Go figure!