Regarding the "Extra Lightweight" version of the 1886 that Winchester made (half magazine, shotgun butt, rapid taper barrel) would you prefer a 22" or a 24" barrel for 45-70?

22 no question. 20 would be even better.

Barrel length in 22 in or 24 inch is preferred, just like the originals. I have 4 original 1886 smokeless rifles from 1910 on, including 3 in 33 WCF and one in 45-70.
Any weight or supposed handing advantages are lost to an un-needed safety and very poor trigger. You are almost better off with an early Browning copy.
Short barrels in bear country are a losing proposition. The longer balanced barrel aids in cycling the action lever and it adds 150 fps to velocity.

I know the 'tests' you are referring too. It was a ridiculous test IMO. A bunch of guys at a gun range handling and shooting a couple of different lever actions is a lot different than cycling one in a willow thicket with a big bruin bearing down on you.

Some people like long barrels, some like them short, but nobody who has ever followed up a wounded bear is going to tell you that a longer barrel is superior in the tangled thickets wounded bears prefer. Longer barrels are just more difficult to maneuver in the thick stuff. The velocity loss of a shorter barrel is meaningless in those situations. I've used the short Marlin guide gun a couple of times now in DLP situations and found it to be a superb rifle for that type of work.

Have a pre-war Deluxe Model 71 in 450 Fuller with a 22 inch bbl. I guess you could split the difference with a 21 inch barrel.
Weight also is a factor. I also have an earlier Marlin 45-70 with a 22 inch bbl. If you are in the alders with a wounded or angry grizzly,
its accurate repeat shots that one may need. Its personal preference and confidence in the individual weapon that counts.
The Wyoming guide in 2018- NW of Yellowstone near the Wind River range that was killed by a grizzly probably would choose differently
if he had another opportunity. In Alaska, what you are carrying quickly can become one's "bear rifle". Choose wisely as you never
know what will show up at the skinning pile, or around the next spruce-birch bend in the trail.