I would say take spacers and find the height that you like yourself. It is not uncommon for people to ask how to lower the seat or movie it back because they want more clearance to the steering wheel.
I know when I made custom seats for a old Vette, I ended up in a very different spot than the stock ones because that was the location that was comfortable to me.
If you are doing a custom job already, don't feel constrained by the stock measurements.
