I'm 6'4" 215# and have owned Challengers for over 3 decades and also one cuda. My first Challenger, a '70 T/A with a 4 speed, was uncomfortable for me as my left thigh always hit the steering wheel while using the clutch. I never felt like headroom was a problem and other than my left leg and the steering wheel, I never felt like legroom was bad.
My '71 cuda had an automatic and I did feel it was a little lacking in legroom. I questioned if the shorter wheelbase took away a couple inches of front legroom?
My '70 Challenger convertible has an automatic and has a 6 way seat. It's always been a very comfortable ride for me, top down or up (though I prefer down!)
A couple years back I bought a '71 Challenger 4 speed with leather seats. Bought at an auction with no chance to test drive before buying. After I won the bidding, I'm thinking, WTH did I do that for, this damn car will be as uncomfortable as the T/A to drive! But I was pleasantly surprised to find it is pretty comfortable. The front seats in the '71 seem to sit lower than the '70's? Whatever the case, I have no complaints.
I'd be interested in trying out a 4 speed cuda, I suspect that combo might not work for me at all.