that motor has cast pistons and cast rings, thats a downgrade from a normal 86 up 302 and makes for a bad foundation for current or later builds. you already stated it would be 600$ to rebuild yours so you would be wasting an extra 250$ to buy something that is of lesser quality. I could rebuild your bottom end for the same 600$ . out the motors I have here, the 302 needs to be rebuilt, the 306 Im going to hold on to and the 351 Id sell, so I could build the 302 either stock or to your specs or I can rebuild your 306. honestly it doesnt matter what path you take but to buy a short block that has low quality parts and lends nothing to performance is a waste of money and Im sure most will agree.
I will put together some prices for you to give you an idea what it cost to do good rebuilds.