Yep, hd4unm is right. Those front and side emblems are from a '59 6-cylinder, not a '58 V8. I would be interested to know what the VIN says it is. I suppose it could be a '58 with a '59 front clip on it, but then you have to wonder why it needed a new front clip, collision? Anyway, it sounds like you are going to pass on it. I would too. That is some nasty rust in a very bad place to repair.
Personally, I like the looks of the 59-59 Chevy trucks better than the 55-56-57s. But then again, I've always loved the look of a '58 Impala over a '57 Belair.
I do LOVE the look of a '57 GMC though. I think it's one of the best looking front ends to ever grace a pickup.
Good luck with your search!
One more thing, I have both a big back window truck and a small back window truck. I think the big back window cabs look best and they bring a few more dollars but truthfully, I prefer driving the SBW truck. I feel like I'm in a gold fish bowl in the BBW. Not only that but when the sun beats down through that big window, it'll cook ya!