Is it ok if the gg is not exactly same as the focal flance distance?
 

e.g. make the lens be able to focus "further than infinity" and give up some macro ability. So that I can make sure it can focus on infinity. I set up like this in my DIY adapter.

It is better to have the back focus as close to correct as you can get it. For lenses about 50mm and longer FL it does not matter so much but for 35mm and wider, if the backfocus is off, then these lenses may not achieve sharp results.

These lenses will also aggravate any image fault if the groundglass is not square-on to the focal plane. - soft edge.