Agree with Jim: Get Modern SAE 250 wt. from Resorationstuff. com or others, (Penrite, Lubriplate.) close to the original 600 wt. designed for yellow metals.No. Big mistake. Don’t do it.
I used 600W, but found the viscosity would vary too widely with weather, and driving conditions for my liking. Been using Redline 80w250 since June. It’s a GLI-5 gear oil, but explicitly states it can be used in our vehicles. So far, I’ve been happy with its performance. We’ll see how thick it gets this fall in the colder weather.