If the engine hasn't been built, why would anyone want to buy it from a middle man? I would just deal directly with SGP. I'm sure it would be as much if not cheaper. The only thing I can see is getting the the engine faster and getting bumped in the waiting list. I'm sure that I would (and I'm sure SGP would prefer) just dealing with the intended owner. So what if I bought this motor from you and a week later it throws a rod? Will you warranty this? I'm sure SGP would make good, but this is a headache I'm sure they rather not have.
So my question is, why are you selling it on ebay. It sounds like there aren't any parts except for maybe an old engine. If you need the cash, why don't you sell it as is?