We thought we could just replace the mixer which has a 6 3/4" spread. No one makes a 6 3/4" spread mixer anymore, that I have found. So maybe we could swing a 7"? I ordered one from Van Dykes. No luck. The threads on the old mixer differ from the threads on the new one. Not only are the threads different but the threading on the old L pieces are damaged from past assembly. So we are a little nervous taking it apart repeatedly.
The risers have an 11" spread at the base. They are not parallel and widen a 1/4" at the top. So theoretically I could use a mixer with a 6 1/2" spread if one could be found.
The plumbers in their infinite wisdom... determined that the L connectors need to be changed and possibly the risers as well. We have not disassembled them from those larger protective sleeves.
I can't find the parts and the local 'expert' plumbers who purportedly have experience with old plumbing like this are without answers.