"next to impossible"
Halcro was the final inspiration for my setup
https://www.youtube.com/watch?v=tfVk430hwU4&list=RDtfVk430hwU4&start_radio=1
His video proved that the JVC Victor TT101 (mine is a TT81) maintains perfect speed even when 3 tonearms/cartridges are simultaneously lowered providing 3 x groove friction. (Charles Kirmuss would not approve).
You give me yet another opportunity to promote the idea of two tonearms: with my three, friends bring their cartridges here, we instantly compare (as well as compare Mono to Stereo).
This SUT with 3 inputs makes that a simple turn of a knob, select one of 4 transformer windings, or PASS for MM
and make some temporary pencil marks for my adjacent Cayin’s volume knob (which only varies for this purpose).
Shown On Top of my Preamp on a Naturally Ventilated Surround/Stand I designed
https://www.audiogon.com/systems/9703
Above was two fixed, 1 removable headshell. I changed to three arms, all with removable headshells, I couldn’t be happier
IMO, fixed cartridge arms is a needless and limiting idea, I moved mine from long fixed to shorter removable, no audible difference except theory and long arm’s mathematical ’less error’.
The very famous SME 3009 (and 3012) with removable headshells, were and continue to be amazing!