It's a ford truck and in my opinion shouldn't be lowered but the gas tank issue all you would have to do is change the filler neck and there are lots of ways to do that. Easiest is to cut it and re route it. With the 4x4 conversion the holse should already be there for the transfer case so find the brackets and a transfer case that is on a truck with the same wheel base then you could use the driveshafts off of the donor truck. Next is the hard part, cut the floor for the shifter. Then find a Dana 44 front end and it has to have the same gear ratio as the rear that's where your research comes in after you do all that it will have to be aligned. The parts would be cheap from junkyards but the labor is the hard part. You might have to swap tie rods and possible ball joints. It would be unique but it's all about how much effort you want to put forth. Have you considered a trophy truck style? 2wd soft suspension with alot of power.

 

The filler neck is in a different position. You don't want to be cutting and welding a gas tank yourself and it would be cheaper to buy the right ones.