When I first started truing Remington actions (and others), around 1978, I mounted the receiver on a close fitting mandrel and installed a sacrificial sleeve which would run in the steady. The sleeve was glued on with five minute epoxy and trued with the mandrel held between centers. While this seemed to work fine, it was a bit of a hassle so I made up spiders which would serve the same purpose. These were mounted on the receiver ring then trued just as the glueed on sleeves were. The next move was to build a jig of heavy-walled steel tubing which would allow the receiver to be set up so the jig was co-axial tothe receiver bore. The jig was then set up in the four jaw and steady and the truing cuts were made on the receiver. I still use this method, with some variations according to whim.
At the time I was using the sleeve on the receiver ring, I also messed with a cast iron lap with a floating pilot which I would use to finish the locking lug seats but I soon gave up on that.
I started out bushing bolts but soon switched to retro-fitting bumps which I accomplished by using inserts dove-tailed into the bolt body and trued to the centerline.
Prior to all of this, I simply faced the receiver while it was held on a mandrel, then lapped the bolt lugs in. I used shim stock wrapped around the rear of the bolt to tighten it up in the receiver while lapping. I did not bush the bolt early on. I found that tightening of the rear of the bolt in the receiver did reduce the vertical in my groups (by about .050") and think that any scheme to tighten up this fit is worthwhile in a match rifle. I recall seeing one action where the owner/ 'smith had installed four setscrews in the receiver to center the bolt. This approaches the problem from a different direction but I have no reason to think it wouldn't work except that it seemed a little finicky to set up, to me. After forty years and an uncounted number of Remington, Winchester, Ruger, Sako, Howa, Enfield, and Shilen actions being trued, I still have never been able to quantify what improvement there may be, if any. The exception is with the tightening of the bolt which, in that one 40X-based rifle, was good for about .050" inch of vertcal at 100 yd. GD