Having the gas tank in the cab isn't dangerous, it's been there in probably a few million trucks, and how many have you heard of catching fire in a crash? The saddle tanks outside the frame rails (like I have on my truck) are a common source of fuel for a fire
if something starts it. Since I mounted my spare tire inside the bed, I'm considering placing a tank back in that spot. I'm an old man and don't want to lay in the mud to get the spare tire out if I get a flat.
If you want to put in EFI, then moving the tank makes sense, because you can get one to put in the spare tire volume that already had the electric fuel pump in it...if that is where you want to put it. I've seen where people get into trouble using the stock tank with an external electric pump.
The threaded holes for shoulder harnesses on your truck, if it only has lap belts, are in the "B" pillar behind the seat, and have plugs in them. Just pop the plugs and install the other point of the seat belt.
If you are considering anti-lock brakes, I recommend getting the diff out of a truck that has this already instead of rebuilding your old diff...
again. If you don't have a Dana diff already, you can't retrofit other types of diff parts into it.