Hi Gang,
A few months ago I asked a question about the uniqueness of the 70 Challenger light bar. After some research and some bucks on light bars, I have come up with the following:
The light bar for the 1970,71 model year is different from the 1971,,,74 years. The 71 is shown twice as it had a mid year change. The difference is that the dash for the early Challengers had an arch over the instrument panel whereas the later ones were flat across the instrument panel. In the first picture you can see the top bar (1970) is stamped differently than the lower 1972 bar. Look at the upper right hand corner of each. This gives the 1970 its arch.
Pictures two and three give you another view of the differences. In picture four notice how the amount of material above the lens changes from one end to the other as apposed to picture five.
In the forth picture I placed the 1972 light bar in a 1970 dash pad. I know it is hard to see with the shadow and all, but there is 3/8 inch gap between the center mounting hole and the dash frame. In the fifth picture the 70 dash and 70 light bar are mated. The mounting holes are practically flush with the dash frame not to mention the alignment with the dash pad.
Now I have seen some dashes where this issue was forced and the holes in the light bar were stretched out of shape to fit. There are other tricks to make it work, kinda. One could also say it is under the dash so no one will see it if it isn't correct. All of that is true BUT, it isn't correct.
Well that's it. I answered my own question. Now to find a true 1970 rallye light bar. I hope this will help others traveling down this road.