Agree that if it is an antique, NO WAY, and even if its a contemporary maker of some renown you may want to reconsider, but if is a 'rack gun' no worries.
The worst ones Ive seen were cut without much thought to the esthetics, and looked it. The classic lines of these, the proportions, etc. are what makes what they are, and thats why many say leave her long. That said, you can still end up with a handsome piece by doing some eyeballin' and mocking up, sitting back and looking at it. You think 36" is what you want, but maybe 34 or 38 will look better?
On the last one I did, a Pedersoli Blue Ridge (Cabela's version) .32 for the young G-sons I had no nose cap to deal with. The wood forward of the top ramrod tube was my clue to do similar back at the rear tube. I taped it off there and looked at it and considered........then gave myself another 1/2" taped the barrel and pulled it out of the stock. I pushed an oiled patch downbore below the cutting line to keep metal bits out of the bore and would snag it latter to pull out. Using the tape as the line I wrapped tape all around as a cutting line, vised it up in padded jaws, straight and square, and with myself in the proper position and a new fine tooth hacksaw blade, cut it off, taking my time, cutting only on the forward stroke, etc. I should mention that years ago I splurged and bought one of those nice HD upgrade hacksaw frames to replace the hardware store cheapie I had used in the garage for years.
WHAT a difference in control they have! You might want to research a tad on the real proper hacksaw technique too, it ain't just hack away, its almost an art form.
Once the cutoff was complete (leave the tape or put on more to ensure no barrel nicks as you work) the barrel was mounted upright in the vise at a height I could get my small square on each barrel flat. I made sure that oiled patch was still in place (I could grab it with a needlenose latter) and carefully filed the muzzle to eyeball flat to remove most of the fine sawblade lines (this is another reason to use a new, fine blade), then went to checking with the square all around and slowly working down the high points. It goes quickly........once squared up lightly 'break' the sharp edges at the barrel flats and consider the crown and front sight.
I have my tools and techniques for such, but as mentioned by another poster it can be as simple as a round head brass screw. You may want to get to this point and we can pick it up here and move onto cutting a new sight dovetail.