Machined as in having the mating faces shaved so the inside is perfectly round when it goes together? There is a diff shop here that knows their stuff, but I don't know if they can do the machining depending on what needs done. I have not talked to them about the caps.

I have a 489 case with 3.55 gears and a solid spacer. It was clear powdercoated years ago and it started to rust under the clear + it was weeping oil in a few spots so I took it out and removed the clear. I was just going to bolt it back in until I saw the MW caps.

I know the ring gear teeth can shear off and the axle tubes will bend inward under heavy racing. I know a local guy who ran one forever in a first gen Cuda and it wasn't until his car became capable of pulling the front end off the track did he start to have issues making him go to a Dana 60.