I've read that Shimano updated the cable pull ratio on their other series early on but not for Dura-Ace until 1997 with the 7700. Which downtube shifting levers are compatible with their 7400/7401/7402 deraillers?
The 740x rear derailleurs are unicorns that only index with 7400 shifters. I believe there is an SL-7402 downtube shifter.
7400 shifters have a cable anchor routing trick that allows them to work with latter generation RDs, but there is no such trick that works the other direction for RD-7400 et al.
When I bought bar-end shifters for my 8-speed drivetrain bike, I had to select the bar-end shifters marketed as "8-speed Ultegra". Those ones marketed as "8-speed Dura-Ace" are the ones intended to be used by the early Dura-Ace systems. I did not have an old Dura-Ace rear derailleur so I had to use the Ultegra bar-end shifter. I suspect downtube shifters have a similar product naming.
Typically, Shimano has a policy of selling its bar-end and downtube shifters under the "Dura-Ace" brand, but the 8-speed ones intended for regular cable pull ratio had to be marketed as "Ultegra" as they were not compatible with the Dura-Ace rear derailleurs of that time. The 8-speed Dura-Ace shifters are sold separately, being only compatible with 8-speed (and lower gear count) Dura-Ace rear derailleurs.
I don't think you will find any ≥9 speed bar-end or downtube shifters for the old Dura-Ace cable pull ratio as the shift to 9 speeds happened when the cable pull ratio was harmonized.
Today, the new Shimano systems with huge gear counts have lots of similar incompatibility issues. For example, MTB 10 speed systems use a nonstandard cable pull ratio different from MTB 9 speed systems. Road 11 speed systems also use a nonstandard cable pull ratio different from road 10 speed systems. However, the new Tiagra 10-speed system (4700 series) actually uses the 11 speed road cable pull ratio even though the system has only 10 sprockets in the rear!
I suspect you may be able to find downtube and bar-end shifters for 6-speed, 7-speed and 8-speed indexed Dura-Ace systems. However, those products are not made anymore so they have to be new old stock (NOS) or used.
Unfortunately, both you and me favoring traditional shifters (you favoring downtube and me favoring bar-end) have to be disappointed. New bikes with downtube or bar-end shifters are hard to find and if you have some special requirements (such as if you want an electric road bike like I wanted), you probably can't find a bike equipped with downtube or bar-end shifters. As users of downtube and bar-end shifters reduce in number, some day Shimano may completely stop making these durable, cheap, reliable and in almost all ways superior shifters and then we all will be forced to use shifters combined with brake levers and are unable to replace a shifter without replacing a brake lever or vice versa! If a rear shifting system fails to work as intended, I can very easily change it from "Index" to "Friction" and still have functional shifting with my bar-end bike. Unfortunately such a thing is impossible with these "modern" brifters.