[Bob B.]

Well, I can either shed a little light on some of this or make it thoroughly confusing.....
First off, K28 is actually fairly common on GMC's with the V-6 (my truck has one). Maybe it's because of the heavy duty nature of the V-6, or the very small standard fuel filter in the Stromberg carburetor. Or the V-6's tremendous appitite for gasoline! As for standard duty and heavy duty 350's, this is interesting: The 'High Torque' 350 2 bbl. in the upper picture is the version for series 40 and larger trucks, not pickups. No AIR pump, commercial type air cleaner. But, there are actually many versions of the 350 specifically for pickups. I have a '67-'69 GMC parts book, and it breaks them down by the 2 letter code stamped on the block. All the codes starting with 'W' are listed as light duty, all starting with 'X' are listed as medium duty. The list is long, 17 different versions of the 350 4 bbl. and these are all for the 10/20/30 series trucks. There is also a lot of overlap, for instance 'WK' and 'XD' are both 350 4 bbl. with Hydramatics, 'WK' listed as light duty, 'XD' listed as medium duty. All 350's listed are 4 bbl. and regular gas for series 10/20/30. I don't believe the 350 2bbl. engine pictured is an LS8, because the second picture clearly states the 'heavy duty' CE/KE 10 350 did come with a 4bbl.. I think the engine referenced in the second picture would be an 'XA' or 'XW' code with an AIR pump, or an 'XB' or 'XS' without. Unfortunately, the parts book doesn't seem to break the engine down by R.P.O. like they do now. The 350 is the only engine that has both light and medium duty versions, but I believe that is because all 250's and 307's are considered light duty, and all 292's are considered medium duty. To further confuse matters this engine list does not show any 2bbl. 350's, but I am pretty sure they did exist in 1969, and the parts text shows a Rochester 2bbl. for the '69 350. Then there is that 1968 396 with the Holley 2bbl.. Carb. # R4147A if anyone asks. Does anyone have a copy of the 1969 Chevy Truck Data Book? That would straighten a lot of this out.