OP does not want a mare's leg, but a short 1892 without buttstock.
Looking at my Rossi M92 Puma from Legacy Sports International (yes, chiappa or someone else makes LSI's Pumas now).
Shortening the barrel on this 1892 leveraction involves removing the magazine plug screw, plug, magazine spring and follower; barrel band screw, barrel band; forearm band screw, forearm band; the magazine tube should come off with the forearm.
_cutting off the barrel, staying above 16" barrel length
_removing the front sight from the barrel end stub
_recrowning the muzzle
_shortening the magazine tube end proportional to new barrel length
_ reinstalling the magazine end plug (requires drilling a shallow detent hole in the barrel for the plug screw)
_reinstalling the barrel band (requires notches in the barrel and magazine tube for the barrel band screw)
(Probably requires bending the magazine tube a little since magazine and barrel join at an angle to the muzzle.)
_remounting the front sight on the barrel
_sawing off the stock to stay above 26" overall length
_ inletting the sawed-off end of the stock for the buttplate
_shaping the buttplate to fit the narrower short end of the buttstock
and I'm sure I forgot something.
Phew! I'm exhausted.
If it were me, and I'm lazy, I would buy a Rossi M92 Carbine with 16" barrel ("trapper" style with Large Loop lever and saddle ring) and find a spare stock for the Rossi Ranch Hand mares leg pistol which installed on the 16" trapper should be overall about 28". (Rossi M92 Ranch Hand with 12" barrel is 24" overall.) And keep the original stock for flexibility; the trapper with 16" barrel is about 33.5" long.