I believe the fix came about because the poppets would wipe out the cats before their 8 or 10 year warranty was up. It was a GM fix and it came after they ended production on the GMT400. The 4.3 lived on though and the later variants rolled off the line with the MPFI injectors. They snap in place of the poppets and do not alter trajectory.
Thanks - and for the other posts too guys, I'm starting to get a grip of this - at last!
They also impede airflow just like the stock setup.
And that's my main concern here - especially as my incoming air is laden with LPG which is heavier than air and thus to a degree can suffer the same mixture distribution problems associated with carbs. Any ideas on how the airflow impediment can be eased while retaining the CSFI system (which I want as back up)?
All I can think of so far - if it's even feasible - is to try raise it clear. My rear resonator is gone (replaced with a flush fitting pop-off valve - an LPG thing) so I have some height there. My guess so though is that the open mouth of 'shroud' that sits around it on the upper manifold will then create turbulence so no real improvement unless I could some how fill that void. Goes without saying I'm paranoid about introducing anything there that the engine could ingest and cause utter destruction!
On the varnishing of the poppets. My motor has only done 40,000 miles and much of that will have been on LPG. Also, I use a decent fuel additive designed specifically to keep gasoline systems clean so the stock CSFI is what I want to retain as back up. Just re-jigged a bit to improve air flow within the plenum.