c6 r ratio billet servo

which one and is there much to installing them

R-code servo with an E-ratio apply lever. Transmission has to be out of vehicle to replace the apply lever because the pin comes out into the bellhousing area. Just be aware of whose R-code servo you buy, Sonnax and TCI need to have the o-ring register cut down. Sonnax sells a billet E ratio apply lever.

which ones dont thanks

I have used 3 Sonnax R servos in the past year, none seemed to need any mods. Went in smooth and simple.  I also have used 2 Superior servos that have the "tight" fit.

Hopefully Frank will step in and clear things up, I know on my Sonnax I had to cut the o-ring register for the piston to slide in and out without forcing it. It does move more freely but found out Friday that it still does not move as freely as it should and will be cutting the register deeper before it goes back together. I know several people have called Sonnax and told them of this issue maybe they finally rectified it but I bought mine 4 years ago.

When I installed a Superior Super Servo, it did not require any machine work, it slid right in the servo bore. Frank advised me to re-use the factory "P" servo spring, great advice because the shifts are crisp with no flare whatsoever. I always have heard/read the Sonnax servo needed machining to operate correctly, maybe I just got lucky.

TCI super servo works great for me in a well used trans that has 15 seasons of racing on it. No mods to install it. I couldn't tell you what lever is in there. I hope to freshen and rollerize it this winter. 

I bought mine back in 2008 so things may have changed. I bought mine through TCI but found out when I questioned them as to the supplier that it was a re-boxed Sonnax. Just a good idea to check the fit regardless.