A833 lubrication

Pardon the dumb question, but what's the best lubricant to use in an A833? I've done some reading on this but there is a lot of difference of opinion regarding use of ATF, synthetics, gear oil and the like. It's all very confusing.

Frank Adkins in his Chrysler Performance book suggests motor oil, something like 20W 50.

Any suggestions?

The climate here is best characterised as warm.