[Mr_Rich]

When you have a failure so early I'd suspect the work that was done on this engine and I wouldn't trust it or the "mechanic" who built it. BTDT, and it was with a mechanic at a Chevy dealership 25+ years ago. After my experience I found it easier to buy a 350 crate engine at a local Pontiac dealer and installed it myself on the street outside my apt. at the time. That engine was still running strong for twenty years until I swapped it out for my spare that had fresh seals and lower miles as one of my retirement projects. Were any shortcuts taken and less care or time taken reassembling this long block? Probably a teardown and inspection will tell the tale. It could be a cracked block and 1000 miles isn't enough to reveal some of the damage yet other than the overheating. My factory 305 in '89 had a cracked block which led to my troubles at the time.