Sounds like all you're missing is Bristol Spline.
Those seem to be
I've never seen Bristol spline tools in the form of hex insert bits.
rather old; the only place I ran into them is in a
1950s vintage
THere are 2 common-ish places to find them in classic computers. One is
in Friden flexowriters, the set screws (grub screws) in the belt pulleys,
etc, are Bristol Spline. The other is in the PSU/monitor area of the IBM
5155 Portable.
A friend told me they're also common in IBM typewrters, but I've never
had one of those in to repair.
-tony