Is this the right BB replacement?
 

A local shop installed this BB back in 2013 before I started doing a lot of stuff myself so I never really looked into it until now because I think I need to replace it because I keep getting a clunking/knocking sound and I don't think it's the freewheel though maybe it's the pedal spindle I dunno.
Anyway, going to try to replace this and see what happens.

is this: https://planetcyclery.com/shimano-bb...xoCxKsQAvD_BwE
(btw this appears to be a pretty hard to find size)

the correct replacement for my current:
https://cimg4.ibsrv.net/gimg/bikefor...9e99ad8ea5.jpg
https://cimg6.ibsrv.net/gimg/bikefor...8d532b357b.jpg
https://cimg7.ibsrv.net/gimg/bikefor...330bb379b3.jpg

Yes I measured the spindle length with calipers, it's 107mm. English threading, right?
Weird how it has a piece that snugs against the outside of the BB shell on the drive side, but sits inside the shell on the non-drive side. Is that normal for these vintage bikes?

Thanks for any help.

Looks like a normal cartridge square taper bottom bracket. Most likely English threading - does DS have left threads and NDS right threads?
There is also JIS vs ISO difference - most likely it is JIS.
The one you linked looks good.

https://cimg0.ibsrv.net/gimg/bikefor...5acfb1252.jpeg
I just did a bottom bracket and yes you are on the correct glide path. A small hint though: I got frisky and just had to have an aluminum non drive side piece. No plastic for me! Mistake…..the aluminum one had deeper threads than plastic one. As I ran it in the spindle started to bind. Ugh. So…get the new BB but if you get binding head to the local bike shop or recycle shop and get a less deep NDS

For just $9 more you can get a higher quality, made in Japan one: Tange LN-3922 Square Taper Bottom Bracket – The Bikesmiths

thanks all. ordered it this morning!

Marginally less here: Tange LN-3922 Bottom Bracket | (benscycle.com)