The receiver ring is straightforward, with the correct tooling.
If Weaver type bases are being used, the rear base is more complicated.
I use a Forster jig for these d&t jobs. Last 99 I did, I installed the front base. Applied a straight edge to the top of the base, ran the rear base along under the straight edge, until I knew where it should sit, fore and aft. Once I knew where it should be, I located one screw hole position, and drilled and tapped it using the jig. Installed the base, located the second hole, drilled and tapped it using the jig.
An internal mike can be used between the anvils on the jig to get the spacing; I prefer to work using the actual base.
A one piece base would be easier. Locate and correctly drill and tap the front holes, then install the base and locate the rear hole.
Using a jig like the Forster pretty much guarantees that all the holes will be in a straight line. Unless you do something stupid.
Wouldn't even consider a job like this without the jig.