I haven't found 366-1690-00 pull tabs for less than twenty dollars each, before shipping. Since I bought most of these plug-ins for twenty-five bucks, that seems a little much. There are a couple of folks selling laser cut tab pull replacements for much less, but it isn't clear whether they are the 1690 or the 1851 version.
On the PS503A, I have a different latch (photos attached). From the manual:
SN B010100 - B025429: 214-1513-0 (release), 366-1422-01 (pull tab knob), 214-1840-00 (pin)
SN B025430: 105-0719-00 (release) and 366-1690-00 (pull tab)
I don't have a plug-in that uses the 1851 pull tab.