I had posted to this earlier but deleted it for not having anything major to contribute.
I also have a base s200 device that Ive had for a few years. I was able to get mine to work on a Transcend 1GB 80x card I had from my old Watchguard XTM 5 firewall. I've also tried the 1.36 disk image linked earlier in the thread and while it worked, it had a number of bugs in the VFD. First was a strange flickering between various bits of text "invalid address" and blank spaces on the hardware clock status "page" on the VFD. Also, when it finally synced/locked over GPS (I have the symmetricom 12v antenna), I got either "REF: " or "REF: Pkt Err". Further testing shown that even without an antenna or network link, it would lock and sync and show Stratum 1. Loading the image on the factory card also yields very strange intermittent errors in the admin pages. I have since rolled back to 1.10. I did ask around if there other versions available, but I haven't found anything or heard back.
However what I'm really after ultimately is the more advancing timing oscillators and outputs that are lacking on the s200. So I've decided to probe around my s200 with my "new" scope (ds1054z) Ive only used a couple times and see if adding the jacks would even work (especially at 15 bucks each). Gives me a reason to probe something. And yes, I found the signals, 10MHz signal, PPS & IRIG. I have a few other items that can use PPS.
With that said, mine only has the TCXO, and I've ordered a Vectron MC597X4-040W that was shown fitted to an OCXO version earlier in the post as well. Regarding installing R121, to me it looks like its just a jumper and not so much a resistor. To my old eyes the pictures look like the value is "000" but I can barely read/do smd stuff to begin with.
I still have yet to dive into mine much more than some probing and CF card testing. I have several other 512MB cards that don't work either because they're too small. I also havent ordered the bnc connectors at this time, that will probably come next week.