Are they supplying the chambers or are you supplying your own to be modified?
I am buying them and having the work done. I will be having one made first and install it in my machine and run it to confirm fit before I would have him make more. Quote is in the works
Have them check the profile of the thread nose area against an original.
Does anyone know if the tools used on the original D2 precombustion chambers will work on the D4 1s1970 chambers?
I just bought (eBay $15) a pre-cup tool for my 12A's 1957-1960, D315 D4's and D315 D6 that has about 15-20 splines and the earlier D2's used the square shank the later D2's I'm not totally sure about so I'd say it depends on the year of the rig.