Awesome, but then I'm biased!
I do take issue with calling it "very few options".
I always contend that the GTO option alone takes a '64 Lemans out of the realm of "low option" but in your case, I count at least a dozen options (seat belt delete was an option so gotta count it!). In my book, that qualifies as pretty well equipped.
The Rally Handling Kit added the Quick Ratio manual steering box and the HD shocks to a GTO. Other Tempests also got specific Springs and the larger dia. front stabilizer bar with this option. But the larger bar was std. with the GTO option and no special Springs were offered for the GTO.
The steering linkage shock absorber has been discussed here from time to time.
It is not obvious what triggered the installation or if it was even a factory installation. It did not seem to be related to the Rally Handling Kit. One of those items that just has never been completely understood. It was only intended for use with manual steering (std. or Q.R.) and many if not all may have been added by the Dealer to address wheel "kickback" complaints. But there is no PMD documentation discussing it that I'm aware of, for service or factory installs.
Welcome to the '64/'65 world here, look forward to learning more about your GTO!