Don't take me wrong... I'm not trying to put words in anybody's mouth, correct me if I'm off base here??
There is no 4.125 "Kit" (currently) available that has
proven significantly superior longevity to (what I've Posted,,, my personal documented experience) the Nicasils???
The S&S Cylinders seem to be a favorite, albeit as Don has Posted in a Custom Order Configuration, Dimensions, then add Custom Pistons, then taking the Custom Pistons and having them Custom Coated, Line2Line, and Custom (or Special Order) Ring Packs... Nothing anywhere near "off the shelf" here...
While I commend you Builders for trying to figure out a "solution", your criteria for "they last" might be different than mine, and what I've experienced with my set-up... "What we felt were the best Components available at the time" Again, don't get me wrong,,, acquiring reliable data on something like this is pretty much impossible at your (mine too) level,,, so many variables...
Only now are we (publicly) seeing the MoCo do this on scale with the M8s...
S&S certainly has the "horsepower" to try / develop different Cylinder / Piston / Ring combinations yet they continue to support the Wiseco 2mm 2618 Pistons,,, Is cost the only consideration??? Surely there are there other reasons??? Good Luck getting a straight answer on that one,,,
As a Consumer, I have neither the resources nor the wherewithal to attempt to develop a solution with Custom Components, so I will stick with "off the shelf" Components and try to get the best service life that I can...
In a prior life, I have participated in R&D with OEM Support, but at this stage, I will leave the R&D to folks that know more than I do, to Builders such as yourselves...
As you have both wished me; "Good luck, and hope it works out for you" (and your Customers)...