As several others have said, you need to be 100% certain that you have hydraulic lifters, and that the block is suitable for those (as Mike just said). What is the stamped number on the machined pad, just aft of the distributor, sort-of behind the dipstick? If it's there and it's a '54 block (you may have to wipe off some dirt and oil to see the stamped number), it should have a serial number ending in F54 with one or two more trailing digits. The final digits should ID if it was originally a standard transmission or powerglide block. If it's a standard block and not modified, fitted now with hydraulic lifters, that would be a problem.
Now, assuming you have hydraulic lifters and the block is OK for those for the moment, from what you stated a few posts back, the valves are probably still set too tight. Rather than adjusting from when the valve just closes, you need to adjust from when the rocker just reaches zero lash. You can do that as the manual states, carefully and one cylinder at a time, setting each cylinder at the top of it's compression stroke, loosening the adjusters for that cylinder's valves, feeling the push rods for side play, and tightening back to remove the side play. When tightened back to the point where the play is just gone, that is the point of zero lash. Although the service manual says tighten an additional 1-1/2 turns, that assumes the lifter internal piston is free to move, and is at the top of its travel. There was a late '50's Chevy instruction that suggested only tightening 3/4 turn from point of "felt" zero lash. You may wish to try that - after you confirm that you have hydraulic lifters.
But one thing still bothers me. A couple threads back you had a sticking lifter or valve. Although you reported you freed that lifter/valve, the fact that you were running the engine with a stuck valve or lifter makes me wonder if either valve or pushrod is bent. Something had to give from what you reported, and I never saw that answered in the earlier thread. If it were my truck, I would to do a compression test on the engine, since there are continued problems. You may find you have a problem with valve sealing in that cylinder.
