Adding ambi and size of lower receiver

[devbro]

I am in the quest to add ambidextrous fire selector to my guns. After getting the first set of gear-sets for this, they proved to add too much width to the gearbox to be inserted safely :|

So here is my question that I hope to fine an answer to before ordering new parts:
Are lower receiver with ambi different than generic ones? Specifically is the inner width wider? Are there special groves for this that I need to carve?

Has anyone else been working on something similar? Any challenges or advice that you are willing to share?

[Styrak]

Any challenges or advice that you are willing to share?

Yes, buy a gun with ambi selectors, or a receiver/gearbox that already has them installed.

[devbro]

my goal is to do it myself. There is no fun in getting something that works out of the box.