Manual lense to EOS full frame bodies

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I have been doing my research online, and nobody has really been straight forward at all.

I know there are a few adapters for older model lenses to EOS bodies, but I know some of their sizes differ and infinity focus can be lost.
As of now I know that most m42 lenses don't lock up the mirror within the full frame models. I am looking at the Yashica ML lenses, namely the 50mm 1.4, and so on. I know these can be adapted, but have seen that apparently you have to use one of the Chinese brass adapters shaven down to 1.4mm. Can anyone direct me to the correct adapter that maintains infinity focus, while keeping this lens away from the mirror with no filing of pins or adapter involved. What I have come up with so far:

High Precision AF Confirm Contax to canon lens adapter | eBay

Maintains infinity focus, but nobody is really clearing up whether the lens pins have to be modified, or if you STILL have to shave the adapted by filing so that it is able to focus to infinity with these specific lenses (yashica ML). Let me know.

Thankies.