Nice. I think you'll like your GM8.
Definitely squirt some oil over the bearing and give it a spin. If you're still unsure, turbo shops usually check the condition of a unit for free.
Next, I would start fabbing an intake (or pick up a 6.5TD setup), then an airbox, an exhaust, and so on. Just keep acquiring parts as the pocket book allows.
Is this truck parked, or is it a DD and you are going to have to do the swap all at once in a weekend?