440 engine build failure

above poster may have nailed it
the cam bearing bore after install by the factory
number 3 is usually tight in a BBM you have to use a bearing scraper and hand fit if you replace the cam bearings I think the spec on that bearing is .001 tight
darn
I'd stick the BHJ tool on it and check the lifter bores and sleeve if necessary
before EDM we ground a flat on the lifter to give some additional oiling (some Buicks came stock with these- not my idea but it works) used a mag plate grinder with a v block
quick and fast
but IDK if it would have helped as quick as OPs lobe went bad
as I mentioned above I've had it happen with s sticky guide but he says heads ok
IDK sorry