As said above, the tube scopes used on Pedersoli/Sharps rifles are what you're looking for and can be bought from Henry Krank.
The adjustments are made through the front mount, so you have to think whether the rifle you're intending to fit it to can accomodate a very forward sitting mount - and also offer a rear mount that's sitting on the same level ( as in the case of a Sharps rifle ).
The two versions we've had, have been pigs to fit, zero and to hold zero ( although this has been on .45/90 and .45/70 rifles ). Optical quality of the two was suprisingly very good. The reticle was a fine, simple cross and a good, clear, crisp image is there.
Nevertheless the mounts the first model came with, required remachining ( almost remaking ) due to their fondness of spitting out the locking screws and losing the zero.
The barrel of the Sharps Quigley model and Long Range had to be drilled and tapped so the mount would attach. I imagine this being a costly operation, depending on your gunsmith like
POI still drifted after all manner of solutions, therefore accuracy suffered and enjoyment with it. In the end, the diopters went back on, the tapping on the barrels filled back in and reblued, both scopes sent back to dealer - and scores going back up to what they were before....
Therefore they've only offered novelty value in all honesty - and at £300 for the one version and over £500 for the other, that's not a cheap novelty. Definatley something for a dyed in the wool scope user with a lot of time, patience and money in my opinion.

Craig