I'm 6'2", 34-35 inseam, i.e., long legs, longer arms. A reach a heavyweight boxer would have.
I have Halls 2" dropped pans, both sides. Engine intrusion cover reduction. 1-1/2" relocated pedals. Adjustable (height wise) steering column.
I also have Halls recovered modern stile Pantera leather seats, and they sit on 90 something Taurus power seat platforms (with power lumbar).
I can put the seats flat on the floor or rasise them about 2" via the power platforms.
I will say that for me (at 200 pounds) the cabin is now huge. On the floor the driving impression is that your eyebrows are even with the top of the dash.
I would say to do it all and thus have the option of adjusting it to your liking. Wilkinson quick release steering hub (worth every penny) too. Mac's short throw shift delrin shift knob too.
All these things help with finding squiggling around room.
What all this does is give the ability to wiggle around rather then have the option of only one driving or passenger position. With this set up it is actually possible for your passenger to be somewhat reclining and catch a nap on a long trip...if it wasn't for those overhead speakers, and those huge 180 degree headers, and that long duration solid lifter camshaft and, and, and ...well I think you get the idea?
As far as 6'8"? I would say probably yes BUT getting out of the car you might need to climb out head first with the length of those legs. Can't do nuttin' wid' dem doors though?