Greetings Chris!
Towing with an automobile, you will definitely want a receiver style hitch with weight distribution and sway control (IMHO). I towed primarily with automobiles from 1980 through 1995 when I purchased my first truck-based tow vehicle (there was one two-year stint where I towed with a GMC 3/4-ton van - - 1983-84), and weight distribution is an absolute necessity with the springing commonly found in the Marquis and competing cars of the period. I found sway to be more noticeable with my auto than my truck-based vehicles, and I suspect that in great part it relates to the weight and physical mass of the light-truck compared to the automobile. Personally, I would recommend the
Reese Strait-Line Hitch with Daul Cam Sway control - - I have used this hitch system exclusively since 1995, and utilized the similar hitch without Dual Cam Sway Control but with friction type sway control prior to that. Just be prepared when shopping for the ball mount/weight distribution bars - - many shops will try to sell you 1,000 pound weight distribution bars - - with your coach you won't want any heavier than 600 pound and I would suggest 500 pound bars (the 600 may be the lightest currently available as my 500 pound bars are nearing 20 years of age).
I suspect that you are going to have difficulty finding a bolt-on hitch to fit your Mercury. Lately, there are very few receiver style hitch packages offered for automobiles of any type. What you will likely find is the situation that I faced with my '75 Cadillac Edlorado - - a custom weld-up hitch. It can be a real challenge to find a welder who is familiar with hitches who is still willing to weld-up a hitch for an automobile - - I talked to many who refused the job due to liability fears before I found a gentleman who routinely created weld-up hitches for those involved in farming, and the hitch that he fabricated is a near work of art in the way that it fits the car without calling attention to itself. Basically, a welder will take a
Receiver Tube with Collar, and add square tube and flat stock to create the receiver which in my case was then bolted to brackets welded to the frame of the car.
The one item that hasn't been mentioned that you will need for your towcar, and that is a good set of rear view mirrors. They aren't as common as they once were, but some trailer dealers may stock some of the less expensive varieties. My favorite mirrors that I use with both my Cadillac Eldorado and GMC Suburban are
McKesh Mirrors - - they are costly, but will last for many years (the set that I have for my Cadillac are more than twenty years old and have required nothing more than a re-webbing kit that is available from the manufacturer for less than $20. You can see the Vintage McKesh Mirrors on my '75 Cadillac Edlorado in the photo below:
Be prepared for some surprised looks if you tow with an automobile on the Interstates - - I think more than a few drivers were shocked to see a 29-year-old Cadillac pulling an Airstream on I-80 just before I took the above photo near my former home in the Quad Cities.
Something that you will also want to be prepared for is that the '66 Safari may very well have a Bargman connector that is not wired to the modern standard and it may also have round pins rather than the flat blades of the current connector that is in common use. The coach is likely wired to the
1966-1981 Airstream Bargman Plug Wiring Diagram while your tow vehicle will lkely be wired to the current
industry standard wiring diagram. While it is a personal preference issue, most wire the coach's connector to match the modern standards used on current tow vehicles. Basically this means paying close attention to the functions of the wires in the Airstream's umbilical cord rather than just the colors, then wiring the connector based on functions rather than colors to match the current standard. Both of my coaches needed to have their connectors rewired, and despite my lack of do-it-yourself skills, I was able to complete the Minuet's conversion in a little less than two hours (this included carefully testing each of the wires on the Airstream with a 12-volt garden tractor battery and alligator clamps to verify that it matched the Airstream schematic which it did).
Good luck with your project!
Kevin