Classification, change detection and NDVI using landsat 2 (MSS), landsat 5 (TM) and Landsat 7 (ETM)

I have 3 Landsat images for the same area. One in 1972 (landsat 2 mss), one in 1996 (landsat 5 TM) and one in 2010 (landsat 7 ETM). I would like to detect changes in land cover and create diachronic maps. Also, I would like to calculate NDVIs and compare the results between the three dates. Landsat 5 and 7 are easily comparable because they have common bands. However I don’t know what to do to make the Landsat 2 comparable…Normalized them?
Also I have another question. Do you usually run first a Maximum Likelihood Classifier and then calculate the NDVIs on the MLC resulting image? Or it should be a separate process?
I use ArcGIS 10.2