If it originally had a 10mm plug this will work fine but if it originally had a 14mm plug thread you can not drill it out larger and still install a 14-10mm adaptor. The hole will be too big. You will have to install a helicoil and then use a 14-10 mm adaptor. Another problem with drilling out past 14mm is that you decrease the seat area for the sparkplug.

Here is a picture of how I repaired my ZDZ 60 when I broke off 2 mount lugs. I decided to remove all the lugs and put the backplate in a lathe and machined a diameter on the backplate. I then machined a ring with the same ID as the OD of the backplate. I then welded the two together and drilled holes radially in the ring for mounting to firewall. It worked perfect but care must be taken to not warp the backplate or have porosity in the weld. I had my welding done in a welding tank and the actual weld was done under water. No warping!!! If you are welding in open air it is advised to preheat both objects to 500- 700F before welding depending on thickness of material.

Maybe you could apply this technique to your DL engines.
It is probably 5x stronger than those damned cast mounting lugs!

Speedy