Rocker arm pad to valve tip is one of the highest contact stress interfaces in the engine, though on these old powerplants less so.
I wouldn't recommend hand filing - small errors could easily spike the stress or create an edge load condition.
If you do go ahead and do the work by hand, check the valve tip after running to confirm that the contact patch has not moved to the corner break on the valve tip.
Bill
1947 3100 Advanced Design
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