torque converter/stall, help

I need a stall for my 727. I'm putting it behind a 408 stroker. I went to a transmission shop today to inquire about the stall, and the guy wanted to know if I needed on that was balanced. My engine is internally balanced

This is my first mild performance build, and I don't know a ton about transmissions and converters.

The builder, who I cannot get hold of right now, said I needed a 2500 stall for the engine.

What information do I need to know when buying a stall/torque converter and selecting the right one.

I've heard some good things about B&M's converter.