Well there is a TD146 and there is a TD146 IV (I think)
I'm not sure because I've never seen one. They did what I call a type II of a lot of their TT.
TD166 and the then the Type II slightly smaller footprint.
It's an older Thoren it will be fine. I've used the belt style for 35 years and the 121-124 for 50 plus years.. My favorite. Right there with Russco, QRK and Sparta for me.. The smaller footprint like a 166 II is a great TT too.
145,46,47,50,60,65,66 parts are everywhere. The tonearms are good quality if they have been taken care of.. Two or 3 kinds. Aftermarket, like you said Jelco, SME, Lynn, Micro Seiki. Repair kits for motors, suspension, plinths, vibration control additional tone arms. Most parts are interchangeable, Quack Quack..:-)
Did I mention I have a crap load of Thoren STUFF. LOL
Have fun ay..
Regards