So as I read this, it would make no difference where the lifters that are loosing prime are located in the block. Closer to or farther from the oil galley should make no difference as the lifter design controls it's drain back and loss of prime. I follow the oil viscosity line of thinking, just trying to understand why this loss of prime only effects a couple of lifters.
Location within the lineup should make very little to no difference. Especially if the oil pump is new or was checked at time of rebuild.
Why only a couple? Because those were machined with greater (internal parts) tolerances than the others. That extra tolerance and a cold engine (and probably a break-in oil or multi-viscosity oil) combine to make those collapse enough to make noise until the engine is warmed up and at that point 1. tolerances in the lifters internal parts change 2. the oil viscosity changes 3. those two changes make the lifters act they should again. If the lifters were really out of whack (meaning the tolerances were much too large...and this would still be very small numbers we'd be talking about), then those lifters would allow constant valve clattering no matter whether the engine was cold or warmed up and no matter what viscosity oil was used.
