Well, I seem to have solved this for the time being!
A guy at work asked me if I was still looking for a go kart. I told him "no", I had already gotten the Phoenix Baja for my daughters. But, go ahead and get me the info on it (I thought I might post it here).
He comes back with an email saying that it's a Manco 710E! Not only that, but right after he got it, the engine seized up. So, under warranty, they replaced it - with a 13HP Robin! They told him it's all they had in stock.
So, I've got a Manco 710E with a 13HP engine coming! According to this guy, it only needs the usual from sitting - a new belt, new tires (bald), and clean the carb.
It does have a bend in one of the front roll/crash bars as his son nailed a tree limb with it. But I couldn't beat the price. He says to me, "just give me a few bills for it when you get your taxes back"!