I've been running Valvoline diesel oil in my '46 for 35 years without an issue or any additives. Actually has a full pressure '54 235 in it. Started with straight w30, but that got hard to find so I've switched to 15w-40. Engine has about 85,000 miles on it since rebuild back in '86 and doesn't smoke at all. The diesel oil has a bit of the additives that you don't get in gas engine motor oils.
David B.
