I use Carburetor cleaner to clean out minor dirt inside and out. If passages are blocked then alcohol to soften blockage so they can be blown out. Uncle Max sells a special tool for soaking the emulsion tube, idle tube and power valve passages with alcohol, tool also assist in blowing them out. There isn't much you can do about corrosion maybe clean with Mauriac acid or liquid toilet bowl cleaner is another acid. Do a search here on fordbarn. If using any strong chemicals be careful and protect yourself! If you send the Carb. to Uncle Max (Max Musgrove) send it dirty, he will clean it properly.
The original Ford resistors are good, even used ones. If new or used, I make sure to clean all the brass attachment hardware plus the two resistor mounting tabs both sides. The resistor is only 0.5 Ohm and dirty hardware or tabs can easily increase the resistance to double what Ford coils need and connection resistance can lead to heating in the wrong places. After only a couple of minutes of energizing the resistor, the temperature is so high it will quickly burn skin if touched. This is normal.