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I'd view the ball bearings as more gentle solution than threads to block the holes. Threads always carry more risk of propagating cracks from their form rather than a peaned ball arrangement. I should be considered that the potential blocking with sludge can be serious in terms of oil distribution. If the crank pathways impede the volume of oil in any significant way the pump when meeting this resistance can blow the pressure relief valve open (this is to save it's own drive mechanism from potential hydraulic locking of oil pathway) too much of this can obviously starve the crankshaft and bearings, but just as serious is the interaction of the pressure check "jets" going to the head. These must be capable of containing 60psi as that's what they do in separating the pressurized crank from the open bath camshaft area. If the oil pump pressure relief opens, it's likely that no oil will be pushed into the head while that's happening. It'll also be worse when cold as the oil is thicker. Part of rebuilding would sensibly cover this off surely?