You'll need a set of metric allen wrenches for that front sight set screw. Get the globe slid in to the dovetail, so that its pretty well centered and tighten the set screw. You may want to gently peen the top of the dovetail on each side down just a tad to help hold the sight in place.
Also don't dry fire without a snap cap or such in place, that'll kill a firing pin in nothing flat. Leave the hammer down and set your trigger and then pull the front trigger in lieu of dry firing.
If the eye cup on the tang sight isn't one of the adjustable Hadley type, so you can open the aperture to a larger hole, you may need to open the hole with a drill bit. You need to be in good sunlight to see clearly thru the tang sight.