I'm installing a MP electronic ignition conversion in my 70 Charger. I'm putting the ECU under the dash since I like the engine compartment to look stock. The MP ballast is a different resistance than the original ballast an it is a different style. It doenst use the bracket that the original one does.

Does anyone know if square original looking ballasts that use the metal bracket are available in the same resitance that that MP one has?

First I'd ask what coil are you going with? The ballast with the orange/chrome box kit is a nominal 1.25 ohms & the race ballast is a nominal .25 ohms. Actually you have a fair amount of leeway on how much ballast you use. I'd ohm the current one & post what you get & if using the same coil maybe trying to get pretty close to that ohm amount. FYI 2 single ballasts will fit side by side perfectly in the 4 terminal "dual" ballast connector(s), the one with the 2 white bakelite connectors, one on each end with the blue loop of wire on one end. If you add a blue loop on the other end it will in effect make em parallel which'll lower the ohms which may help you get where you want to be. The last 4 terminal ballast I checked had 6 ohms on one side & 1.6 ohms on the other side & when I made em parallel I got 1.1 which was pretty close to what I wanted with an OE black ECU/stock black coil

Right now it has the original coil on it but I'm replacing that with a MP restoration coil.

The orignal ballast is about 1.5 ohm and the MP one is about 0.8.

that ballast will be fine. don't try to over-think it. the difference between them is so small it doesn't matter. but i would not suggest going as low as a .5 ohm. as Rapid said ideally you should look for something between 1 and 1.25. lower the ohm, the more current flow and that creates more heat.

I had it backwards. The origianl points ballast is about 0.8 ohm and the MP one from the kit is about 1.5 ohm. I went to the parts store and found a 1.5 ohm that has just a small tab formed into the ceramic that I can grind off and use the original mounting bracket.

If the ECU in the kit is orange in color it wouldn't hurt to carry a spare one (not orange) in the glove box. A parts house 4 pin generic Mopar ECU is fine (& cheap)