Pete, If you can't get a good thread in the there, you can use a helicoil, or a E-Z LOC insert. They have them for all different sizes.
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1970 T1 W/MassIVe 2913cc RAT/?EFI? w/direct fire (very soon) and 915 trans
1962 SC 1776cc SP 944NA brakes, 993 wheels
VKG