After taking the cam out of the box, lean with mineral spirts, I like a moly lube that stays on the lobes, insert cam and cleaned with mineral spirts lifters/tappets, rotate cam by hand and watch for each lifter to spin in there bores.
If a lifter doesn’t spin, it’s a problem of a badly machined cam lobe OR a badly machined lifter OR the bore rod the lifter is out of round.
The rest of what you wrote is all I ever followed. Break in oil, a pint of high zinc additive if needed, prime the oil system. (Did you rotate the engine while priming rod is spinning?)
I just had my first cam/lifter failure ever earlier this year with a Summit cam. I used a cam I had intended for another engine as it’s replacement. A Comp thumper, the little one.
Zero issues.
IMO, finding 30 year old lifters is a crazy hunt to go on.
On the flip side, purchasing a roller cam suitable for your build may be hard to find one that suites the build. Even more so when it’s a solid roller cam. A Hyd roller cam can probably be found since they can be found small in size, comparatively speaking.
