I'm not sure that good/bad #53 casting idea is necessarily correct. After that post last year, a fellow TDR member and I spent a Saturday afternoon comparing the castings on our particular trucks and one other that was with us that day. From the info that thread referenced, we determined that we both had the "good" block castings. His promptly cracked on the dyno not too long after that. Now it is perfectly feasible that we mistakenly identified the blocks as the "good casting", but I don't thinks so.