I am always curious Tim, wanting to know more. I do not put as much faith in detergent vs non-detergent as you do. A bypass system with 1/8" NPT (small) lines that is reduced to 1/16" and oil pressure is 15 psi (216) or even 30 psi (later) is just so slow and insignificant, I can't see much oil moving through it at all, let alone claims of it passing all of the oil over time. Any system that depends on splashing from driving creating enough current to mix filtered with unfiltered to fight for its turn to be close to the inlet of the pump is just antiquated. Which IT IS!
Fastforward to 2015 where we now know, with 100% certainty that Bypass oiling (like splash oiling, etc) is insufficient and a primary cause for premature engine wear. Since it's so easy at machine shop time to modify the new style 235's and 261's to do what modern systems are so successful doing, it's the best $100 you can spend.
Even if Bypass is your only choice (due to your rule for keeping it stock, economics, or it's not machine shop time), putting the filter up on the manifold, causing even more strain on the pumping system seems like another weak link. Putting it as low as the oil pan so it doesn't have to work its way upward twice seems prudent.
Crankcase gasses mix with the oil, dirt is introduced through the slits in the cover, road tube (since it's negative until you drive 30mph) and then all the dirt has to pass through a 1/16" orifice on a bypass schedule. It's all preventable using what GM has learned over the past 50+ years.
On one of my trucks I don't care about any of that. Like some of you, I want to keep it 100% stock because being a good steward of the hobby means doing the maintenance required to keep it in perfect condition as they were when they were new. Who is so lazy they can't change the oil and filter at regular intervals?
ME! The daily driver I am creating will not be like that at all. It will use only as much modern technology as is necessary for as close to maintenance free as possible. How much fun can one person possibly have?
