These are some very cool up-closed photos of an OEM and NOS REPA shoulder-belt brackets mounting kit, as used by the factory 914-6 GT ("Gurthalter" in German translates to "belt holder").

Maybe there is a typographical error on the part numbers. The Porsche factory manual for the 914-6 GT https://pbase.com/9146gt/image/23060692, on the last page of the manual https://pbase.com/9146gt/image/23060741 shows the harness mounting brackets as pn 914.502.903.71 with a quantity of 2 for the same part (driver and passenger). However, these photos show a slightly different part number, off by only one digit; pn 914.502.904.71 https://pbase.com/9146gt/image/149455782. The question now is which is correct; the March 1970 Porsche published parts manual, or the label attached to these parts bags. In reality, the part number difference to me is insignificant, what matters to me most is the fact that we now have an excellent visual reference of the original parts kit that makes up the REPA shoulder mounting brackets.

By the way, here is a good photo showing the very same hardware installed on the very famous #40 Sonauto 914-6 GT https://pbase.com/9146gt/image/22265176