One thing to consider is what you are going to do with the compressor after you finish your truck. Your photos look like your truck is in about the same shape mine was. I can tell you you will have a bunch of blasting to contend with. I am running a 3.5 hp and a 2.5 hp hooked together and a 40 lb. harbor freight pressurized sandblaster and have no complaints. The valves on the sandblaster were crap but were replaced with new ball valves. If you are close to one of the Hudson's dirt cheap locations Mississippi they resell harbor freight returns. I bought the 2.5 hp compressor and the sandblaster at 90% off. Both needed repair but the ball valves were cheap and the compressor needed a head gasket that I cut from some copper flashing. All of that to say you have some time to shop two small compressors can drive a sandblaster and unless you are going to be rebuilding something after the truck you can get by with 2 that will work out to total 5 hp or better. I only have to run one most of the time then kick the other in to blast. When I get finished with the truck I can sell one and keep one around to pump up the tires on the lawn mower. I am in the market to replace the 3 hp but that is another story.
http://www.tptools.com/StaticText/AirConsum.aspx This link has some useful info. This is a diagram of how to plumb the air system proper plumbing to control the moisture is magic when it comes to running a sandblaster
http://www.tptools.com/StaticText/airline-piping-diagram.pdf
