I'm 6'5", about 280 and not as limber as I used to be.
I have replaced the bench seat with buckets from a 2002 Mercury Mountaineer. They are mounted lower than the stock seat and create a nasty angle for the brake pedal. I don't have the truck on the road yet so I'm not sure how it will feel.
I've removed the gas tank and have the seat backs up against the back wall. You don't seem to gain too much room from removing the tank because there is a ridge that runs along the back wall at the top of where the tank used to be. My seat back hits that before I get to use the newly found space at the bottom.
Guess I'll have to put subs in there.

I'm 5'9" 165 lbs. I have plenty of room. My buckets came out of an eightysomething midsize Olds wagon. They're small, and the seatbacks are pretty thin. I experimented with the height before I built the stands that I mounted them on. Even with a stock steering wheel there's plenty of clearance. Normally I drive with the seat forward a little, and reclined back. I'm comfortable.... Oh yeah I sh!tcanned the headrests.

I'm 5' 11" and 175 lbs. and using an 80 something
chevy bench seat without headrests and orignal steering wheel. No complaints for head room
really, and much more comfortable than the coverless original seat
with decomposing foam that would cause a dust storm when it was sat on.

The way I mounted it, the seat runs out of room before it runs out of
track. I don't know if this is normal for these seats, but they have
a wider seat base than the original bench seat. I don't know if I'll
ever remove the gas tank, but am interested to find out if this changes
anything.

I'm 6'5" 280lb with bucket seats out of a 94 full-size blazer and the steering wheel is a little close to my legs and rub when I make large turns but other than that, I feel comfortable in it. It's the only thing I've driven since I got my license 6 years ago and anything else feels funny to me.

6-5'' ABOUT 200