3 speed allison?

[BlackedOut67shorty]

Ok I'm just confused when I went to the auto parts store to get a tranny filter with gasket, I told them my 67 c10 and they pulled up two automatic transmissions, the th 400 and an Allison three speed which I don't know to much about. Thought it was a fancy name for the th 350 but when he pulled out the gasket it was square but with a small square notch cut out instead of the slant cut the th 350 has. I got the right gasket when I just asked for a different year but I want to know more about this 3 speed Allison transmission. I haven't herd to much about it and I wonder if anyone knows info about it
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