I have a 54 chevy with a 235. After driving for over an hour, a hydraulic lifter definitely gets noisy. If the engine is shut off for 5 to 10 minutes and restarted the noise goes away until another half an hour of driving. The lifters are new. I know there is tech information on this problem. I have read Tom Langdon's tech tips. I would appreciate any additional information.

What has worked for me and a lot of people I have helped is to cut a shallow groove on the bottom of each push rod to allow air to escape from the lifters. Here is an example
1950-52 Chevrolet's had this done from the factory.

The factory hydraulic tappet doesn't pressurize the pushrod (as the V8 etc. does). There is no oil pressure outlet at the pushrod ball seat.
The tappet is designed to self-purge of air bubbles by having the highest point of internal oil pressure at the point where the plunger is secured by the snap ring. The air is continuously pumped out by fresh oil pressure from the galley.
I would guess the slots direct drain oil to the bottom of the cup to improve the ball's service life.

1950-52 lifters had a hole in the push rod seat as do most aftermarket lifters.
I have been through this so many times.

Fair enough. If his 1954 has 1950-52 lifters, he can bleed the air out with slotted pushrod ends.

Does he have 1950-52 lifters?

Do you know why "most aftermarket lifters" have holes in the pushrod seat?

I wish I could talk to a lot of the people that engineered parts for these old Chev's to know what they were thinking.
I have done extensive research on 235 hydraulic lifters and have found that every time people, including me, have high speed lifter noise it is from aftermarket lifters with a vent hole in the push rod seat. In all of these cases notching the push rods cured the problem.
I am working with a test engine right now that is not drilled for hydraulic, and I am running hydraulics's in it.
If this works out, as it seems so far in my test engine, I will be able to install hydraulic lifters in Chev's as early as 1929.

Which hydraulics are you using (or is that a secret)?

235 lifters, or are you asking brand?
From 1929-62 Chevs used the same OD on there inline six cylinder lifters.

That's a scary thought right there: they simply made the .990" body to suit the 235, and used the same plunger (with the oil feed hole to the pushrod) as the Gen-3 194, 230, blah. Rocker oil through the pushrod is very common, even Chrysler went to it in the later small blocks.
It's safe if the pushrod ball is a good fit in the cup, meaning you won't lose oil pressure.