Since this comes up regarding those older engines that are non-roller check this out 1248 ppm http://pqiadata.org/Motorcraft_15W40.html about $18 for a 5 quart jug at Walmart.
I use Amsoil Z-Rod ... it has high zinc as well as rust inhibitors to last 2 years in storage vs the 1 year of conventional oils. It coats the block when the engine runs and then prevents rust from forming when it sits for months not running from condensation, etc.
Shows 6/2018 as test date FWIW, Amsoil Z-Rod is 1400ppm https://blog.amsoil.com/do-older-vehicles-need-high-zinc-motor-oil/
I have no dog in this hunt. I use Lucas 10-30 Hot Rod oil. Zinc content is 2100 ppm on their last update, 2019, on line listed specs. The 1956 y-block recommends 20w oil so in my opinion I will not go to any oil which indicates it will act like a 40w. Stock engines do not have a high psi valve springs which would put a higher load on the cam lobes and lifters. The oil can be used and is formulated for flat tappet cams and valve springs with a lot higher than stock Y-Block for sure. I change oil once a year and cut up every filter. I have never witnessed any metal in the filter or on the magnet I have epoxied to the drain plug. Your experiences may differ.
You sure about the 2100 ( not 1200?) 2100 is very high - too much is not good, just as is to little. A 10-40 oil will not hurt anything and some run 20-50 with no problems.
One of the reasons the diesel oil had/has more Zinc was due to the ***mins 5.9 / 6.7 still having a flat tappet camshaft. They didn't need much due to the fact the redline was around 3500 rpm so didn't need much valve spring pressure, did need some extra due to the exhaust brake. One of the very last flat tappet gas car engines was the 4.0L Jeep inline 6 which was phased out after 2006 timeframe. Most everything else went to or was roller cams after that so high zinc content was not needed. Zinc caused issues with some emission equipment and was greatly reduced even in diesel oil but I do run 15w-40 Delo in my old cars including my Y-Block without issues and have for many years. But then I am not running high valvespring pressures/excessive lift or high rpm on any of my engines. If I am breaking in a new cam I refer to the instructions from the cam company and they usually recommend some sort of additive for the first run in. After that I don't run anything but out of the bottle oil.
I can only read what is on their website under Hot Rod oil specs as you can also. “Your experiences may differ”
https://lucasoil.com/pdf/Zinc_Values_MotorcycleOil.pdf https://lucasoil.com/pdf/TDS_HotRodCl***icCarOil_10W30.pdf
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