never, ever, had to make any alterations to receiver or chassis on the top bearing surfaces.
I have however altered the front and rear bearing pads of the trigger groups to achieve proper tension without milling the 1000.00 sage chassis.
The M14Doc / M14Doctor , which is me, is retired from all things firearms related when it comes to business so sorry I can be of no help.
an explanation of the problem and perhaps I can walk you thru it.
No offense to notsorichguy, I'm sure he know his schit, but I've fit several dozen sage rigs, for both individuals and for professionals using them for work and always ended in success. from the early navy seal versions (grey with AR buttstock) to the newest models available in Canada and no modifications were made to fit the receivers. except for the trigger points I mention above.
but then again, there's a first time for everything so let's here some details if you can OP.