Another option is to have a stud made with a slightly increased OD – quite a common practice for similar problems on classic cars. Depending on the diameters required this will give you a stepped stud so the spigot will still fit through the manifold: ~ a descent engineer should be able to supply the same in the appropriate material.
Completed this on a few cylinder heads without any problems but the taps & dies I have are all imperial (mainly BSF) so not much use to you.
HeliCoils may also be worth looking at for damaged threads.
Good Luck.
Last edited by Bob Meadows; Nov 21st, 2019 at 16:45.
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