The issue with the hydraulic lifters currently sold for the 235 motors is that they seem to have a relatively high rate of failure. They collapse prematurely. One of my best friends runs a machine shop. They rebuilt a 235 for a customer and used new hydraulic lifters. Motor broke in just fine. Had a couple collapse within 20 miles. Replaced the offending lifters, darn if some of the new lifters collapsed and one or two more of the existing lifters. He replaced all of them, failure again. By the time he called me, he was ready to give up. I gave him a set of nos gm and that solved the issue.
The lesson here is if you want to run hydraulics and you have the ability to hunt down some nos gm or USA replacements (sealed power, Elgin, trw, Johnson) from 20 or better years ago, that is probably the route you want to go to get the best results.
The mechanical lifters, both early milk bottle style, and the later style do not suffer from this problem so new replacements are fine to use.
