Both the 20 moa rail and the 20 moa unimount would be too much unless you are shooting waaaaaaaay out there. You probably would not be able to get a "0" less than 400 or 500 yards. Stick with one or the other at 20 moa, not both.
I would think the unimount would fit on the Ken Farrell rail, but not sure. I have a Farrell rail on my muzzeloader built on a rem action. It is good base, no problems there. However, I prefer a rail with slots the full length as I often use the ones toward the center to mount things like a level and / or angle cosine indicator
. Those type of things can be mounted on the scope as well, so the center slots are not necessary....... comes down to personal preference.