Converter stuck in cranksaft!

What kind of fluid should I use. The thing is, I don't know what they had in it to begin with?? Like I say, they are closed for the weekend to so I can't ask them.

I did go to a auto store and they recommended ATF Dex/Merc.
I won't be starting it for a few days (assuming I fix this problem!) anyway.

It's a 1972 904 Transmission.