The design of the early stovebolt hydraulic lifters did not provide a pathway for trapped air to be purged from the lifter bore. Later designs used a tiny pinhole in the pushrod seat to allow for a small leak to happen, which allowed the trapped air to escape much more quickly. I have seen several modification procedures to the lifter and the bottom of the pushrods suggested to create a very small amount of leakage to accomplish that kind of air displacement. BTW- - - -Lincoln Zephyr V-12 engines in the 1930s and 40s also used a very primitive design of hydraulic lifter, and they had similar problems with noisy lifters on a cold start.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!