A 58 block huh? Does it have a steel line behind the side cover? The reason I ask is that GM changed the oiling system slightly for the 59 model year. So you could have a 58 casting date for a 59 model year car/truck. that block might not have the steel line as 58 was the last year for the steel line. That may or may not be a consideration here. May or may not be part of the problem, or it may be part of a much larger problem as Jerry suggested above, poor assembly of the lower end. Were the rear most lifters pumped up? Which lifters were collapsed? Any chance you used newly manufactured lifters as opposed to NOS GM or RNOS aftermarket (25 years old or older)? For whatever reason, the new lifters on the market have been a bit of a challenge. A close friend of mine runs a machine shop. Did a 54 hydraulic motor for a customer. Three sets of new lifters before he called me. Could not get a complete set in that motor that did not have a few that collapsed shortly after start up and run. I gave him a set of NOS GM lifters and that was the end of that. This issue with the new lifters has been going on for some time.
