This is a link to another discussion on Diesel oil in gas engines, this time the Jeep 4.0 which also has a flat tappet cam (yes, I realize the 4.0 isn't a Model A engine).
There were one or two posts about it's effect on catalytic converters. Been awhile since I read it but I remember it was very thorough.
https://www.cherokeeforum.com/f2/rot...essing-188168/