Not sure on exactly what short blocks will work, see if you can find a bare block or just the block and parts from a junk yard or online, such as craigslist.
My main reason for replying is that if I where you, getting all of that engine and extras and a truck for 1500 bucks sounds pretty good. The truck might be useless, but you could probably still salvage some good or decent parts from it and the engine stuff to do the LS swap. If it were me I would get the truck as soon as you can, salvage what you need, want and can from it, then cash the rest in for scrap. Alot of those LS swap parts and stuff will run alot more than 1500 bucks if you try and buy them new, even used they are still expensive. Some elbow grease and a car trailer might get you some useful parts and some extra cash from scrap.