I am 6'4" and feel your pain.  Unfortunately, your options are going to be limited to what you define as "major modifications".......  Even if you find some appropriate seats you are still going to be limited in your leg room and the stock steering wheel hampering you getting in and out.

When I first bought my jeep, it had a similar setup to yours with stock cj7 seats bolted/welded on to the base of the 3a seats.  While it gave me a tall back seat, it didn't look "correct" and it was next to impossible to get to the toolbox without taking the passenger seat completely out.  It also was not that much more comfortable than my stock seats as they still had a very sharp angle on the back.

The real issue is the wheel wells.  One modification I have seen several people do is take a chunk out of the wheel wells and move the seats back 2" or so.  To do this, you are looking at some decent sheet metal/body work.  You can't go too much or you might get into the tire some when the suspension flexes.  Then you can put in a tilt steering column, relocate the gas tank, find some nice racing seats, add a roll cage..........................see where I'm heading? 

At some point you have to accept the fact it is a vehicle that was designed and built in the 40's and 50's.  In that day and age, it was a marvel that you could travel somewhere in some form besides horseback.  The definition of "comfort" was much different than it is now.

In the end, I went with stock seats with thinner 2a style seat cushins.  I still have my knees in the dash and the steering wheel in my stomach.  However, at 45 mph with no top, manual brakes and manual steering I am ready to stop and take a break after a 40 minute drive anyway!

Good luck and post photos of what you come up with!