If you ever look at a photo of the inside of a 917, 908, 910, etc. in period, you'll notice the steering wheels weren't fastened with a flush head ALLEN drive bolt, they were attached using 6X domed, slotted Titanium screws.
I was able to dig up the vendor/part number for Stainless Steel screws that we used at Porsche for our 917 restoration to replace the unsightly looking black oxide allen drive bolts for MOMO steering wheels. No, they're not titanium, but titanium would likely be too pricey even for the 911 guys....
$9 shipped for a set of 6 screws.
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