Steve,
Unless someone else can satisfy you in the meantime, I can go to an old SUN catalog I have with all the particulars and get back to you tomorrow eve. I don't think any of the "Super Tachs" required a sender, but I can confirm later.
Verne
If you look at the instructions for the sender, it lists model SST-700. That probably means I was wrong about the SST only being the 800 series, but it looks like all 700 series need the sender, as Joe originally said. The other sender you pictured is (I believe a '70). There's even an ink stamp date on the box for one.