In all probability, the DeVille that you mention will be a good candidate to tow your Safari-23. From the factory, it would have had the 472 cubic inch V8, Turbohydramatic 400 transmission, and its standard differential ratio would likely have been 3.07. Several optional differential ratios were available, including an "economy" 2.73 ratio.
With a pre-1970 engine, my biggest concern would be the potential for valve recission as the '69 motors weren't equipped with the special hardened valve seats to accommodate unleaded fuels. For a "show and cruise" collector vehicle that is under minimal stress there may be no particular problem, but it doesn't take much towing to produce stesses and result in valve recission -- it took less than 1,000 miles towing with my '65 Dodge 383 cubic inch V8 before recission became evident -- the cost for a total valve job with new hardened inserts was just under $2,000 in 1980. The 1970 and later engines had factory hardened valve seats, so it would be possible to install a later set of heads if necessary.
Since the DeVilles of this era were rear wheel drive, it shouldn't be a tremendous problem to change the gearset; but when I checked into this two years ago, my mechanic indicated that the particular differential used in the late 1960s early 1970s DeVilles didn't have a large number of ratios available when new or aftermarket. With my Eldorado, I found a recored radiator to be a virtual necessity -- ended up going with a custom to get the most cooling capacity utilizing a 4-row heavy-duty core -- the car now runs cool under all conditions. I also went with a large Hayden transmission fluid cooler as well.
You will need to find a hitch fabricator as there aren't any stock-bolt-up hitch platforms for Cadillacs of this era. Locating a hitch fabricator was among my two biggest problems in outfitting my '75 Eldorado Convertible as most hitch installers no longer do fabrications -- the kits are available, but for various reasons (liability most often cited) the shops don't want to undertake such projects. I finally found my fabricator through my regular mechanic -- the shop specialized in agricultural welding and would handle hitch fabrication in the "down" periods.
I love driving my Cadillac convertible both solo and when towing -- it has no particular problem with my Overlander, but it is at the top end of what I would want to tow with the car and is also at the top of the 6.000 pound trailer tow rating published in the car's owners' manual. Had I been planning on towing when I purchased the car, I would have held out for a DeVille convertible as the Eldorado had 2.70 Final Drive ratio that is cost prohibitive to change with the only other ratio being 3.07 (due to its front wheel drive configuration) -- not to mention the virtual impossibility of finding wheels for the FWD Eldorado that aren't bent to a degree that they produce vibration when driven. The DeVille has wheels that are shared with other GM divisions so there shouldn't be a particular problem finding a replacement wheel if one or more should need replacement on the vehicle that you are considering.
Good luck with your investigation!
The photo below is of my '75 Eldorado with the '64 Overlander:
The phot below is of my '75 Eldorado with the '78 Minuet 6.0 Metre:
The photo below shows part of the Reese Weld-Up Receiver that was fabricated for the vehicle: