Grandpa's 1948 truck

[mr48chev]

That's a pretty loaded question reddragon. simply because on a truck like that in that condition it's who's selling, who's buying and how bad the buyer wants it and why.

A guy who's really into the big AD trucks will probably give a bit more for it especially if he has access to a good replacement engine. Some guys are only going to want it for what appears to be one really nice 48 GMC cab to use on a 1/2 ton pickup.

The Ford bed may be worth something to a Ford guy who is hunting that particular bed for a truck he is restoring. I've seen a few of them and they are a really good looking flatbed frame. Having it on the GMC doesn't knock anything off the value of the GMC though.

I have no idea on what kind of price to put on it. I get sticker shock every time I see old vehicles advertised for sale lately and feel that I'm a bit out of touch price wise.
Your location may have as much to do with it's price/value as anything.

I would however clean it up inside and out before putting it up for sale. Even to cleaning up the engine and engine compartment even though it most likely doesn't run. A nice shiny and clean truck with all the tires aired up just looks a lot better to prospective buyers when they walk up to it the first time. That they can hop up in the seat and not worry about getting their clothes dirty is a plus because they will want to. It''s also easier for them to sell their wife on the idea of buying it rather than trying to tell her what that dusty truck with the greasy engine compartment and load of scrap wood on the bed will look like when the spend a few thousand more dollars on it. And they may not try to knock you down on the price as much as they wold the way it sits.