Where to start with a rusty block?

I bought 3 old rusty 8 3/4 pigs really cheap because they were 489 and 741 cases with 3.91 and 3.54 gears. They wouldnt even turn ! Been outside for years....
Well anyhow... I was at the bar and got talking to this OLD guy that used to be a machinist. He told be to soak them in Deisel and Acetone ( fingernail polish remover) for a few weeks . Said he did this with old tractor motors often.

It Worked ! Even the gears cleaned up ! I tossed the diffs (open) and bearings but used the housings and gears...