IIRC the Kestral is a (wide body Eagle) and it "will" fit the 1st gen Tundra AC, but "not" the DC.
I think it mostly has to do with the DC cab height being a couple inches taller than the AC and/or possibly some differences in bed depth. I'd get some very exact measurements from the seller and compare it to your truck.
Here is a good side by side comparison of two 1st gen Tundras in each flavor:
http://www.expeditionportal.com/forum/threads/24681-Haggis-Multi-Use-Tundra-Build/page5
I think you can see in post #48 that the DC body is just a bit taller and wider.
Looks like a good deal on the pre-owned FWC. There's a reason they get snapped up fast.
When I was considering a FWC a while ago I believe they said the Hawk was the appropriate camper for the 1st gen Tundra DC.
I would contact Stan @ FWC for the exact scoop/info before making an offer.