I don't know how easy it'd be to mask the internals of the hydraulic lifter but the concept was only to increase the lifter diameter by a thousandth or two. I did not think plating the inside of the lifter bore was practical as the block is big and heavy, plus there are many more surfaces that'd need to be masked. The lifter body itself should be more do-able.
There is another factor which is cost. If the cost to plate 16 lifters is too high, then it becomes more practical to sleeve the lifter bores.
Reportedly the electroless nickel coating is very hard. This may provide an advantage to the lifter face.
It is only an idea that could be pursued by an interested party.
