[Pyrotechnic]

I took a look at the link in your sig and it looks like the truck has some sentimental value to you and I completely understand.

That 4x4 truck looks really nice! Rather than make a Frankenstein of the two trucks, I would suggest using that 4x4 truck to make a clone of your Grandpa's truck...make it just how you remembered it looking when it was new! It would be sort of a tribute to his truck.

As for his truck, get it out of the elements and keep it as is. Clean it up, get it drive able and mechanically sound.

This way, you can have a nice looking truck that would remind you of his old truck, but every now and then you can fire up the real one and go drive it!