anyone balanced a stock 360 crank?

Internally balancing helps crank & bearing life a bit because there's not that extra weight hanging out on the ends, especially in performance & higher rpm applications. It's not necessary, but certainly doesn't hurt. OEM balance can be off anyway and if you changed the rods and/or pistons, it can throw it off even more. Use lighter rods and pistons and you might be able to get by with minimal mallory metal or none at all!

You still should balance it even if you keep the external OEM balancer and converter weights to make sure it's "right".

The B&M flexplates are nice if you keep the external balance weights.

If the balancer/damper has a pulley WELDED on, THROW IT AWAY IMMEDIATELY!
The rubber already deteriorates over time, but welding around it certainly hurt it more.