You would have to check with Ed about all this. But from I know, he gives a 3 mo warranty on all the parts he sells. A reman sensor (which only lasted for 1.5 years for my dad...how long did your stock GM one last?) will typically only have a one year warranty. And Ed does advertise on his ebay parts that they are tested. So they should work when they arrive. They are usually they work, or they don't.
I have never got any bad parts from Ed. On the rare occasion I have heard of someone that does, he will send them another part ASAP. He has a really good reputation for great customer service.
As for email tag, just call him. Phone number is 216-671-3736. Then you can get the part, pay for it, and have it done in no time. Not saying you should go with Ed. Just saying, if money is tight, he is a really good alternative to get the part for half price. And he has all original GM units. Nothing rebuilt. Nothing reman.
But as a thought, does the MAF from your impala work in the GT? I think they should. Then you could drive the GT until you get a replacement MAF (I saw your rant thread.)