For some cars, I just switch to anti-freeze when it gets cold. I did put anti-freeze in the Cobra when we trailered it cross-country, but drained it when we got out of the cold winter mountains.
On the
oil, I would just suggest checking it. A 210F water temp shouldn't break down the
oil. We had been running various synthetics and changing them every race since we were losing a little
oil pick-up, but we have since then realized that even with the hot race temps we just aren't damaging the oil. Now we run straight 30W and change it every couple of weekends. Our typical NASA race weekend usually consists of about twelve hard 30 minute sessions and the oil seems to be holding up just fine. We do overfill the car slightly with oil in order to help solve the pick-up issue and it has been fine.
The 3-link is a HUGE help, especially if you are learning on this car. It isn't faster, but it makes the car much more predictable so that you can right-foot steer. Suffice it to say that I believe that if FFR had the 3-link on the original spec racer, it wouldn't have scared so many people. The original spec racer was one of the hardest cars I have ever learned to drive.
Sounds like your car is just fine! Glad you had fun!
-Dan