I'm 6'1" although with longer legs compared to torso and it's very similar to original seats. I have 3 inches head clearance to roof in normal driving position.
There is a photo that shows original driver seat and recaro passenger in the collection.
I didn't measure original seat cushion height from floor but it's 6 inches for Recarco's. That's at the back part of seat cushion to the lowest part of floor. The front is raised but that does not influence headroom. Front is approx 12 inches and with seat base of 20 inches that's a angle approximately 17 degrees. I might up that with more spacers.
I have minimal spacers and slightly more at the front to increase sloop front to rear. Approx 20mm at front and 10mm at rear. You could remove 2 to 4mm without cutting the carpet. Some spacers needed to allow for carpet, some to allow easier fitment. The runners are not heigh and the mounting plate is 3mm so fairly minimal base height.
I'll a couple more photos to the colleftion to aid.