Manual (split image) focus screen for 5D Mark III

I'm frustrated with the focusing screen on my 5DIII for use with legacy manual focus lenses.

I understand that the standard focus screen can be replaced with a split image focusing screen, and I've found some resources demonstrating/describing how to do this. But I'm loath to do it myself for fear of damaging the camera or misaligning the placement of the screen.

Has anyone had this done on their 5D3 camera? Do you have recommendations for repair places (in the US, preferably) who do this well? With the split-image focus screen in place, does AF still work, are all AF points still visible and useable?

Thank you for your help!

I've experience with the Ee-S and the Eg-S screens for my 5D and 5DMkII and they are both quite easy to install.

From memory swapping screens is not a (Canon) User option for the 5DMkIII, so I assume these are third party (permanent) options that you are seeking, and I have no experience there, but what might be useful to you is this earlier conversation - I kept it in my file because it mentions that the Eg-S fits into the 5DMkIII - I understand that is not a split screen.

The links in that older thread might be useful also.

WW