Installed a Sparco Roadster seat with modified Nagisa rails. The seat is basically an Evo with lower sides for easier entry/exit. It's a little wide in the back, but some kidney pads would do the trick. The rails are the (somewhat controversial) Super Low Single Lock ones. While only one rail actually locks, it's super rigid. Standing on the brakes, I can't get the unlocked side to budge.

A headroom measurement is taken by measuring the distance between the seat surface (where your butt goes) to the headliner directly above. A sunroof car like mine is already down about 2" in headroom. With the GT-R seat, that measurement was 35". With this new setup it's 37.25"