Yeah, I think this was discussed some time back here, and the consensus was something like ATF & a possible solvent or something.

I recall about 20 years ago buying a '58 Plymouth - a warehouse find - that smoked enough (oil) to kill every mosquito in the County. I mean, bad.
My buddy, who's actually quite the wrench, old racer, and collector, did an oil change with a bunch of MMO in the mix.
Ran the thing for awhile, and it quit smoking. I drove the car around a bit afterward because I couldn't believe it.
I'm still amazed by that.