I know the Blinder M-20 comes with 2 heads, and the M-40 is 4 heads. If I were to purchase the M-20 and later add 2 additional heads, where could I get them. I have heard the M-20 is identical to the M-40, minus the extra heads, and the M-20 should be sufficient for a small/medium sized car. I assume the "replacement lenses" aren't the same as additional jamming heads. Am I right?