This is my great grandfathers old toolbox.
Thanks for making me feel older than usual today.
Assuming what you've got is a 6-drawer top box and a 5-drawer roller cabinet, it's the same as the stack I bought new in 1972:
They also made a 3-drawer roller cabinet IIRC.
Look inside the top till, in the left side compartment near the front for a date stamp. It will have a month and year marking. For the roller cabinet, look on the front uprights near the bottom, on the right or left side of the door.
Those were pretty good boxes in their day, as Craftsman box quality goes. If they're just dirty, by the look of your photo, I'd say $125 to $150 tops, and considerably less than that if there's any rust or damage, or if the drawer slides aren't in good shape. I wouldn't take anywhere near that for mine, but it's in nearly-new condition.
The other thing to consider is the historical value, if you knew your great-grandfather or not, or if you want to have something of his. Frankly, I think your uncle should just give them to you, unless he's got a son or grandson who might want them.