Yup parklights in the front fenders under the headlights so front fenders at least are GMC. From the one front hub looks like an earlier (47-48 I think) Style, plus the tank under the bed says 47-48. The fresh air vent on the drivers side is also 47-48.
If you look at the large version of the bottom picture on the left you can see a coil spring and either a broken leaf spring (Odd Angle) or trailing arm which suggest later model rear suspension change. Also the back axle hub doesn't seem to match the front hub. And the weird I'd say homebuilt bed and tailgate. The AD truck beds are pretty simple other than the roll and the stamped spot for the fenders on the 54's. I've seen a couple trucks fixed up at show's with square beds edges like that and they both were homeade. I've even consided breaking some up out of heavier material for my part's chaser.
I'm calling it a Hodge Podge But if I were closer I'd go pick it up just to keep it from getting crushed, I see parts that could be saved and used, Heck I've pulled parts outta worse trucks.
Any of you guys that are close and have a place to keep it should save it.
MONGO