Thanks for that link, it has a 'model overview' table 1/4 way down comparing 3T, 3TP, 4T, 4TP, ZM-4T, and 8TP.
Takeaways: P = simul-focal, 3 = single boom, 4 = dual boom, 8 = swivel arm.
Out of those it looks like they all have the same heads with the exception of the ZM-4T (which is totally sold out everywhere online anyway).
This has answered quite a bit but I still don't know what:
- N means (SM-4TP)
- or the X (SM-4NTPX); comparing on Ebay it seems this means just a Barlow lens with the X? Only $20 more which makes sense.
- or where the SM745NTP fits (especially considering this is the term used just for the head, whereas above the numbers seem to specifically refer to arm type).
I saw a video of someone who said after ringing not even the Amscope reps knew, but that basically there were 2 main heads being used, with everything else being accessories.