Having partly gone through this same problem, I want to note that I tried to figure out which lifters were bad using a stethoscope and listening while the engine was running, putting the stethoscope on the head. That didn't work very well (really hard to figure out exactly where the sound is coming from), and it appears I replaced the wrong ones.
Ross Miller suggested in an earlier thread that the only way he has been able to successfully diagnose which lifter(s) were bad was by placing a stethoscope directly on the valve body while the engine is running and warmed up. Basically the same setup as in his video for adjusting solid lifters on a 1953:
Ross Miller - Speedwell Garage, Adjusting the lifters on a 1953 Another indicator he mentioned for a particularly bad lifter was oil spurting from the valve body itself, as in the above photo.
The basic message is - don't trust whatever you think you hear, if you aren't putting the stethoscope directly on the valve body with the valve covers off and the engine running warm. You may get a false reading, and end up doing the whole process (including removing and replacing the head) again, like I will end up having to do, whenever I find the time again.
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