Cruiserdrew
On the way there
The M1 15w50 is good stuff, but their numbers can not be correct if it is indeed, as listed, an SN/SM rated oil. In fact VOI's of the stuff usually list the zddp levels as significantly lower. API criterion from SM rated oils is no more than 1200 ppm SN (as listed for 15w50) is 900 ppm zddp.
I wouldn't trust it in my 2F.
But the SN limits of 600/800 ppm do not apply to oils other than 0w-20, 5w-20, 0w-30, 5w-30, and 10w-30. Once out of those grades the oil manufacturing companies can use what they like.