As I rack the focuser out it's getting closer to being in focus, but it seems I'm just a bit short. That's why I was thinking I needed another extension of some sort.
I didn't mention this originally but I did order TKP20001 from Land, Sky & Sea. It appears it's too big to screw into anything I have. If you look at the FC-60C system chart below it looks like TKP20001 will thread right onto my focuser, which it does. But I then have nothing that will thread onto TKP20001. I have TKP20005 (at least I assume that's what it is), and the chart says it should fit but it does not.
So I'm wondering what the correct adapter would be coming off of TKP20001 to work with my setup.
That's a surprise because I'd have thought you would easily reach focus with your mirror diagonal having a longer optical path than the prism I use as well as your FS-60C having a shorter metal back focus distance than my FS-60CB.
Mine came with a couple of other adapters that can be used to give more back focus. One is the coupling (TKP20006B) which threads onto the focuser tube, and there's a much longer extension (TKP20001) which connects to that, then it's the TKP20005 visual adapter , TKP00104 coupling, and finally the TKP00101 eyepiece adapter. Looking at your first picture I don't think you have TKP20005 in your setup.
One option would be to get a basic 1.25" extension tube and play around with that until you find out how much extra back focus you need. Once you know the amount you can always invest in the proper Tak adaptors but I'd be wary of spending the money now until you can be sure of what you already have and which parts you would need.