You will also need the clutch for the 8hp, the 14hp most likely had a larger crank diameter, if the engine buyer didn't get the clutch and pulleys.
eBay takes a big chunk, as much as 40% on some items, but the bottom line is that its still the best place to get national attention and to sell many items that would never sell locally. Myself, I'd never list a whole tractor, I'd part it out down to the tiniest nut or bolt. Relist nothing unless its free, and lump all the unsold small parts in the end for a final listing as a lot, all else gets scrapped.
I'd figure that the trans would be worth $50-100, the deck maybe $200-300, the mule drive another $40, the rear wheels, maybe another $75, the front wheels another $50, the hood maybe $75, the fenders, $25-50 if shipping don't kill their sellability, and the rest is potluck as to whether you find someone that needs them that week. Even still, subtract 40% from the list of items sold on eBay and its far more than $100. If the seller of that tractor does do eBay, he's fully aware of this. I've bought various machines for cheap locally and cleared well over a grand per machine on eBay, it depends on the machine, the time of year, condition, and often how much it'll cost to ship. Most buyers include shipping in their total cost when bidding, so the more it costs to ship, the less you make whether or not you do free shipping.
If that were mine, I'd not let it go for less than $250 minus the motor, with or without the clutch, if it had its orignal clutch for the proper motor, I'd add another $40 or so, or what ever a good used clutch would run. I sold the deck from my last WH locally for $300, I kept the motor, sold the tractor hulk for $350, and sold the original chrome hubcaps for a $100. I very well could have parted it out further but needed the room and the WH was the least valuable of the lot of tractors I had just bought.
If I were you, I'd look at putting a larger motor back in it, it'll bolt into the frame and if you do have the clutch from the 14hp, it'll save you another expense.