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The correct finish for your 1970 would be a semi-gloss black finish. I used Eastwoods black paint for brake drums, etc. Or use black engine paint. You need something to be able to handle the occasional drop of brake fluid.
I know some guys have done this, but what type of prep and what kind of paint did you use?
If you're not interested in a stock color, then your options are almost unlimited. I've done mine in hi-temp aluminum and added a coating of hi-temp clear. Looks great.
The usual sanding and a good soapy water cleaning to get rid of any oil is all that is required. Just don't get in a big hurry and let paint dry for a few days before handling.
A wirebrush isn't the best method to clean the MC. I would remove it and sandblast it with AlOx, that will remove all the rust and provide some means of rust proofing (alox embedding), then do as Keith said. A real automotive 2 component paint (paint + catalyst) and maybe a clear coat will give the best result. The aerosol paints will not hold up as good as the 2 component paints. You could also have it powdercoated, the coating is available in almost any imaginable color.