The countersinks where the lollipops attach to the car are not necessary.
The countersink where you press the Monoball into the mount is.
See attached installation instructions.
http://bd8ba3c866c8cbc330ab-7b26c6f3...1TMS~A_INS.pdf
As it notes, the splines will shave off as you press the bushing in.
I can tell you heating a part up in an oven or using a heat gun helps tremendously as does freezing the part overnight that you are pressing in.
This is a Hydraulic press task and not a hammer / socket / block of wood operation to install these.
Last item. Before you install on the car use a good quality sealant or RTV the seal the edges front and rear. The Mono blocks are Aluminum and the mounts steel. Both are bare and will start corroding the aluminum in a few days thru galvanic action when moisture (electrolite) seeps in. Coating the mating surfaces of both parts with wet epoxy primer while you press them in is a standard practice in aviation.