What rpm stall converter should use?

In order to even make a guess, your missing over half of the important information needed to do so. How about some dang details?!?!

Start with the cam specs.

Your also better off with a 904.
I bought the car in February of this year, the engine was already rebuilt, the person said it’s a mild cam, which I can hear, and after market steel cylinder heads. The person was supposed to send me the specs, But you know how that goes I don’t know what the numbers are, he never sent them.