I am steadily making progress on my 1973.5 engine rebuild (I got distracted buying a 1974 911 that was parked outside my mother-in-laws apartment building unused for years). I did the chain tensioner upgrade before I started my 1973.5 with new idler arms with the engine in place and then put 4k miles on it before the rebuild. When I did the upgrade I saw There was galling on the idler arm shafts, but I did what I could with 600 grit sandpaper and careful cleaning. The 4k miles with somewhat galled/sanded shafts arms slightly blemished the new arm bushings. With the giant investment in this rebuild so far, I am taking no chances with those old shafts that already started doing damage. The idea of press fitting in new shafts into the chain housings makes me nervous with the loads those shafts take, so I bit the bullet and bought new porsche genuine chain housings. What is odd is that all dealer websites and Pelican say the replacement part numbers for my car are: 930 105 062 01 and 061 02, but what came from two different dealerships was parts stamped 930 105 101 0R and 102. Does anyone know if the chain cases are all backwards compatible with my 1973.5? And the latest ones I got superseded the website numbers? It seems that way. The only thing I have noticed so far is that they are beefier than the originals,so the two studs that go inside the case need to be replaced with ones 4mm longer to leave enough room for the oblong nuts inside the case.