The rod length does not change with a stroker, unless your looking to do that.
I do believe that the rod length is the same as the OE Harley units. They will measure 7.668" center to center.
GMR Post: If you are looking to buy that kit , I would do a search first. The piston used in that kit is a extremely short set up with the wrist pin that is almost into the second ring. You install the pin & clips into the piston, then a support rail(supports the oil scraper ) then the oil rings into the piston. These kits had piston rocking issues and oil use issues.
Are there other piston options to use with the S&S kit? I was thinking of the S&S kit as the way to increase displacement versus boring the cases such as with the 107" kit. And installing the longer stroke takes care of rebuilding the lower end.