I'm fixing up an old Hallicrafters Tube radio and I look to replace the
original type 47 bayonet lamp with a long lasting LED lamp.

IF the old Hallicrafters is an S-38, some substitution caution is in order.
The pilot light on this (transformerless) model is wired in parallel with
one half of the rectifier tube's filament. If the current drawn by the
substitute lamp is too low, the heater (filament) voltage across ALL the
tubes will be a wee bit higher. Maybe not a good thing for tube longevity.

Old Chief Lynn