A short cylinder can be fitted several ways, easiest of which is to use washer shaped shims where the cylinder bushing bears against the frame at the front of the window, also used to correct endshake. If the new cylinder allows too much barrel/cylinder gap, the barrel can be set back.
On Colt Single Actions, and some copies, the cylinder bushing is removable and can be replaced.
If headspace is too tight, some metal can be removed for the rear face of the cylinder.
There are always more ways than one to skin a cat.
Bob Wright