Our conclusion decades ago when we had to repair some originals is that the final machining of the ends the shaft rides in was probably done after welding.

I sent you a PM.

Thanks Dan for all of your replies. About the small flats you said they milled. Any chance you have a picture of them? I ask because I haven't seen many good picture of the rear arms. On the picture that I have seen I didn't notice any flats but I didn't know about them. Not knowing about them I may have overlooked them. That do you think the purpose of the flats were? A aid to jig them for machining in a jig or mounting flat to a mill table or other? My son thought I should try to machine them after welding. With the machines I have I don't think I could have gotten the job done.

A little info for others needing to build some control arms. Others have said that you need a beefy steel jig to weld these in to keep them in alignment. From my experience of building things. If they could be completely welded in a substantial jig that would not flex when welding in it. It would be very hard to get them out of the fixture and you could never get them back into it. This is due to the fact that as a weld cools it shrinks and produces a tremendous amount of force.

My method of building these. I build an wooden jig to hold all the parts in position . I also made steel spacers to hold the ends in alignment. I would then tack weld them together take them out of the wood jig and check them on a surface plate to make sure they were flat. Add more tacks and check again for flatness. At this stage it is fairly easy to make any corrections. Go back and fully weld. After they are fully cooled unbolt the end eye spacers. At this point you would have a hard time taking the spacers out. If you use a propane torch to heat the outside of the tubes in the area of the cross tubes as they cool the spacers will just about fall out. This is because as heated metal cools it will shrink and pull. Install the bushing and check the fit of your pin. More than likely there will be some misalignment. This can be fixed in a press by squeezing the ends in. After welding the plates and sway bar mounts some small alignment problems will also have to be addressed.
The above is a time consuming process. If you needed to make hundreds of these. Machining after welding makes a lot of sense.

Fixture picture
 

Attachment 31784

Attachment 31785

I don't have any pictures but I included them in my drawings. We believe they provided a firm interface for clamping the assembly into some type fixture. AC Cars used many jigs and fixtures for weldment subassemblies.

I our repairs were did some test welds and determined how much shrinkage occurred during cooling. We then made the "hard points where they needed to be so that a cold final weldment was almost exactly nominal. It worked really well. We built the front half of a chassis in that manner and it worked very well also.

No, we didn't keep our calculations and I gave our 8ft wide 16 ft long thick steel jig table away and a man used it as a bridge over a wet weather creek crossing his driveway. (It was in the way everywhere and it took a small crane to lift it for moving.) The rest of the main chassis tooling went to the steel scrap yard. Over the decades all the subassembly fixtures but one got borrowed by somebody repairing an original car and never found their way back home.

Dan if were to have to build a bunch of these I would also build a jig that would have built in compensation . Thanks again for all your replies!

You are most welcome.