gvincent, those pics are exactly what a factory 400 balancer looks like.
If it's an internally balanced 383, it will have a regular damper on it, and using Grumpy's method, or pulling a head and measuring the stroke is about the only way to be sure. A 383 should have some clearancing on the bottom of the cylinders like Forces mentioned, right where the rod bolts are closest to the bottom of the cylinder.
jt