I don't think an H3 is going to be a good choice to put a WC lift in.. Not for him to roll on the steering wheel and drive at least.. It's not going to be anywhere near wide enough to put a chair there. It's a pretty narrow vehicle inside and the transmission tunnel is as wide as a full size vehicle. H2 would be a better choice I think..
Even if the width was there, I really don't think the headroom is without a LOT of body lift so you can carve out the floorboard deep enough to get the chair in there..
If you're thinking he'll be able to slide into the driver's seat, leaving the chair in the back, like in a van.. The bottom of the rear doors are pretty narrow and once again, no room to get a chair in there and then there's no room to get into the drivers seat.
I'm pretty sure you're going to need to be looking for something with a column shift rather than on the floor.. The shifter on the floor is just going to take up to much room..
Better yet.. Try and find a Ford 4x4 Van and set it up..
http://sportsmobile.com/ultimate.htmlYou owe it to yourself to get in touch with these guys if you're looking to get your sone into the outdoors via 4 wheeling..
http://www.disabledexplorers.com/