I have the same engine with similar mileage on a complete rebuild. It has one lifter which does the same thing yours does. The significant tapping goes away once the engine warms up, then runs as quiet as a mouse.
I had a discussion with pre-68 Dave about this particular issue and he said that this particular issue is not due to air trapped in the lifter and would not be fixed by making grooves in the end of the pushrod.
You either have to live with it or pull the lifter, disassemble and repair it or buy a new lifter.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission