Rather than a hotter plug I think I'd tighten the gap a bit, say to 0.035 and take it out for a long drive to see how they look before letting it sit at idle. You said in your initial post that you carefully returned the Edelbrock carb "to Factory settings". Did you do anything to check that the settings were right for your engine setup, setting idle mixture by the highest vacuum using a gauge, checking plug color immediately after a WOT run (starting with clean plugs and shutting off before going to idle - kick to neutral, shut it off and coast to a stop)? It sounds to me like you're running fuel rich in the mid-range, unknown at WOT and idle.
The Edelbrock 1405 Calibration Kit comes with 6 sets of Metering Rods, 5 sets of Main Jets and Metering Rod Springs. Not sure what the rebuild kit comes with, but thinking none of the above, just gaskets & O-rings.