Awesome! I'm just about to start my 6.0L swap in my 80 -- Any hints or tips?

Did you use the signal coming from the PCM for the speedo, or did you use a DRAC, and just split the signal coming from the transmission?
As far as the gauges go, there isn't really much of an established testing procedure that I've ever heard of... Probally be easiest to just replace the gauge outright...