Could be worn lifter bores. We have been getting 50 year old blocks in and lifter bores are worn bad. Some are wore for different reasons but age and mileage are the usual cause. The other thing we found was lifter bores were in the wrong location But that's another issue.
What I would do is check the clearance on the lifters. A loose lifter bore will cause lifter noise to come on from to much clearance and pressure bleed off. They do make different diameter lifters but usually when the are worn they are out of place or oval. Even new blocks need the bores to be trued at times. Here is a video. The method he uses to fix the bores is not recommended because it will not true the bore only resize it.
But the video will show you how bad they wear. This is always overlooked on builds. and more then none usually a problem on 50 year old blocks
my son has a bhj lifter truing fixture as used in the second video that is the proper way to do the job. something new in the shop
This video will show you the loose lifter bore in a mopar
This video is the correct way to do the job. Without this fixture the bores end up centered where they wore to.
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