Welcome smallshaun! Glad to have another tall man around! I'm 6' 8" myself, and struggle with fitting in numerous kinds of vehicles, including but not limited to, no suprise here, the 2003 series Explorer! (hence why I've never owned one).
I've looked into the idea of moving seats back but generally just choose the vehicle to purchase based on whether I fit or not, but I know that doesn't help you much.
Here is something I've learned though that may be interesting... typically vehicles with power seats go back less far than those with manual seats, I dont know if it is because the motor is in the way of the seat moving back further or just that they have never thought about it. Unfortunately most cars made in the past 10 years or so, the drivers seat is almost power, and to get a manual seat is often either just ordering the base base model or special ordering. Before trying anything drastic though you might try to find a manual seat at a junkyard (not very likely, since 2003 is still pretty new) or from someone who wanted to upgrade to pwoer seats, etc. I wouldn't guarantee it as being always the way, but have noticed that.
Aside from that possibility, I'd probably go with Tony's suggestion of drilling new holes. Unfortunately without looking at the brackets, that may be easier said than done. often the floorboard is molded to a precise location for the seats and the bracket for the seats are angled so you can't just lift it up and move it like you might have been able to in order vehicles.
Another possibility would be moving the seat further back on the bracket itself. Again I dont know that exact model since I've never owned one, so I can't say whether this is possible either, but often the seat bolts to the bracket which bolts to the floor, and the possibility would exist you could modify where the seat attaches to the bracket to gain a few extra inches.
Sorry I dont have anythign concrete to offer.
