Grouping them all as "Ohio rifles" is like trying to categorize all rifles from Pennsylvania the same way.
There are Ohio rifles stretching all the way from the latter part of the Golden Age up into the very late percussion era.
Some are long swamped barreled, very ornate flintlocks and others a shorter, straight barreled half-stocks with practically no decoration.
I do have a bunch of info on Ohio's and a ton more is available from the AOLRC (just google - they have "years" worth of articles available in PDF).
Here is some "fancy" Ohio's with barrels in the 42"'ish range
And then some half-stocks (mostly) with barrels ranging from 34 to 44"
Unfortunately, when someone says OHIO, a Vincent may be the only thing that comes to mind...
So if your buddy want's a 28" straight barreled cap gun there "is" an original Ohio out there that was built that way.
I love Ohio's even if many consider them "ugly"