Peter, it may pay you to have the oversized holes TIG-welded closed, then remachined to 11 mm. Also note that DeTomaso offered aluminum valve stems in the Gr-3 catalogue for Europe- only. These are still available from some vendors- I bought a pair last year. You could also contact Anders Hellburg in Sweden. Anders has a factory-built Gr-3 club-racer and maintains the DeTomaso Gr-3 Registry. He may even have some spare valve stems! Good luck-
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