Rod bolts and cylinder wall failures are the common problem. Rod bolts every two years at least. Never use any block over a 340-4. Castings on higher number blocks are poor quality. 340-8's are junk . The highest I have gone on a stock block that survived for 15 pulls was 593 @ 7200 CHP. The reason it came apart was poor maching work from Ryan. @ Shady Dell Speed shop.