Bob,
There were so few of the smaller gripped 1860s made there may not be any "historical" demand for them. Cimarron and Uberti typically spin "historical" variations to their market advantage.
For instance take the 20" short barreled 1866 and 1873 rifles. There are historical example of such and because the length is handy and offers a heavy barrel advantage over the 19" carbines they produce them. These are some of the most popular barrel lengths and configurations they produce.
They did the same with the Brass "Navy" grip 1872 Open Top, there are actually more historical examples of this than the same grip on 1860 models. Then they make short barrel variants of these pistols which are very popular for modern shooters but their pedigree is dubious. The same is true for short barrel "Sheriff" versions of 1851, 1860 and and 1861 revolvers. The short barrel versions are popular but the accuracy is suspect.
The niche for "Navy" gripped .44 caliber 1860 models is already occupied by the "1851 .44 caliber" revolvers primarily made by Pietta. The very inaccurate anachronisms are very popular if you read the forums on other boards. It meets the fantasy requirements of people who like the octagonal barrel styling, smaller grips and the .44 caliber. Then there is a subset of those who have purchased those pistols with "Confederate" brass frames because of cost. They are the ones who really don't give a hoot about authenticity, yet they want an "old fashioned" looking pistol. That's fine, they are BP revolvers and the reality of it is that most of us are just dressing up like cowboys on Saturdays anyway, so who are we to be judgmental? I like the looks of the "Sheriff Model" 5 1/2" 1860 as well. I know there are some die hard Army model fans who shoot the 1851 .44s because they prefer the bigger bullet. It's all good fun.
There is potentially some good news...you don't have to wait for Cimarron or Uberti to get an 8" version. The front sight makes a 7 1/2" version a bit more difficult, the slot is right where you need to make that cut.
If you cut it behind the loading lever latch retaining block you would have a 6 7/8" barrel like this. You would have to re-cut the block dovetail and shorten the loading lever arm.
That's all a lot of work...You can easily switch out short grips for your Army Model Grips. Sometimes they need fitting, at other times they don't. I had some I used to switch back and forth between two pairs of 1872 Open Tops. I no longer have the pair with the shorter grips. It is possible there might be someone on this forum who would be willing to swap their "Navy" model grips for Army Models.
In conclusion I think the primary reason that Uberti doesn't make a small grip version of the 1860 is because that is part of the identity of an Army model We even call the grip length, the "Army Grip." When describing the 1860 we say, they started with an 1851 frame , made a frame cut to allow the rebated .44 caliber cylinder to fit, added the new swept profile barrel with the creeping loading lever and added the Army length grip with iron back strap. It is part of the major identity of the 1860. The reason they could just add the short gripped variation to the 1872 is that there was no name or identity relationship to the grip and the model. Well that's my story...and I'm sticking to it.
Regards,
Mako