I would pay $1K for a "used" NASCAR block with casting number XE 192540, so long as it isn't hammered to death by previous owners. (sonic check the cylinder walls)
When the NASCAR blocks were cast in Australia, some of the blocks had too much core shift (and therefore thin spots in the cylinder walls which made them useless for NASCAR). Those blocks with excessive core shift remained in Australia and were installed in production automobiles. So a block with the XE 192540 casting number located in Australia is a NASCAR reject! The core shift might be acceptable for your uses, again the only way to be sure is with a sonic check.
However, the NASCAR blocks had 4 bolt mains. If it has 2 bolt mains, it's not a NASCAR block. As I've written before, 2 bolt or 4 bolt mains have no significance to me, as far a Cleveland blocks are concerned, they are both as equally stout. Clevelands do not fail at the main bearing caps.
Just because a block was manufactured in OZ doesn't mean it is a better block. The standard Australian block is no different than the block manufactured in the US. Mind you, some Australian blocks known as "pillow blocks" are supposed to have some of the features of the NASCAR block, you need to visually inspect to determine this. The pillow blocks have raised "bumps" on the outside of the block above the core plugs. The internal bulkheads above the main bearing saddles will be as thick as the bearing saddle all the way up. The internal sides of the block above the pan rails will be as thick as the pan rails all the way up. All 8 bores should be verified with a sonic check report to be reasonably thick, minimal core shift. Cylinder walls should be no less than 0.120" thick on the thrust sides, and if at the limit, the bores should only need a clean up, not additional boring. If the block has all those things going for it, I might consider paying $1K, because it would have all the same advantages as the NASCAR block.
Having hefted a NASCAR block once in my life, I would agree it does weigh about 50 pounds more than a standard Cleveland block. Dan Jones disagreed with me on that issue once, he felt it was more like 25 pounds, I figure he must be in better shape than me!
One last got ya with Australian Clevelands. When Ford of Australia installed electronic ignition in their Cleveland, they installed an electronic distributor made by Bosch. The hole in the block for this distributor is a different size than the hole in our US made blocks! So to run a late model Aussie block, you are locked into using the Bosch distributor, or whatever performance distributors are available in Australia to replace it! The distributor hole in a US block is about 1.56".
Bottom line, before you pay $1K for a used block, a visual inspection to verify it has the heavy duty features you are looking for and a sonic check of the cylinder wall thickness should be mandatory.
Your friend on the DTBB, George