The AC 3 has a Armature that is quite unique being a Hollow Rod produced from both Boron/Beryllium.
My comparisons of Carts of the same design, but with some having undergone modification where one model has Beryllium as the armature, has shown that Beryllium is able to produce a very attractive sonic and in the comparisons, Beryllium is the one I have preferred over Boron, as a general description, the Upper Mid's are able to be perceived with a much improved clarity, at the expense of a tightening of the Bass.
As the Armature on the AC 3 is a unique selling point for the design when originally marketed, I would suggest inquiring if the Armature on the AC 3 can be maintained during the refurbishment process.
There might be much more cost effective routes if Solid Boron become the only option to compete with the original armature on the AC 3.