Harold:
I found the Studer spindle assembly to be compatible to Frida. A807, A812, A810, A820 and A80's spring and three pronged flange would fit but the screw on Frida is 3 mm whereas the Studer uses smaller 2.5 mm screw stems.
Since I don't plan to exchange hubs very often or use 7" reels (other than the cal tapes), I plan to use its original setup - although it is very hard to grab and pull up.
Here's what it looks like for the Frida Mk II reel platform with a Studer spindle:
