If you feel the need of a front sight on a 1917 belly gun, you will have to solder one onto the shortened barrel.
These are safe for modern ammo, but you hear it said that the shallow rifling means you should stick to lead bullets and forgo the jacketed stuff. I wouldn't use +P ammo with either type of bullet, but that's just me. Others will tell you it is safe to do so.
If you are going to make a belly gun, why not remove and save the current barrel unless it is bulged or damaged? Buy a replacement 1917 barrel from a salvage gun and play with that piece. Then you will have both a belly gun and the ability to restore an original Brazilian, a model that used to be cheap but which is getting pricier by the month.
In any event, don't cut the barrel so short that you lose the front locking lug for the ejector rod.