Great vintage MM cartridge for my Nottingham Analogue Spacedeck/Spacearm. Recommendations?

Audionote IQ3m - an upgrade over what you have now with no risk - its the Goldring 1042 taken up several notches.

Yeah, that's what I thought - Nagaoka MP-500 or Audio Note IQ3 if not vintage.

By the way, which one of the two would overall sound better in Nottingham Spacearm ? What would be your best guess ? Or just sound different ?

Unless you are targeting a specific vintage sound, it’s likely best to avoid vintage cartridges as modern cartridges usually perform better.

Assuming @dover’s comment is correct, then it seems a choice between a better similar sonics with the AN or a different but great presentation with the 500.  I favor variety so would choose the 500, then have fun alternating between both carts.

That would be a pain for me. In this case, I prefer constancy, just one cartridge.