Hi,
To bend your tang, just put the tang in your vise on its side, and then use the barrel as your handle and bend it. Much easier than hammering. However, all this is much easier if you made sure to file the under side of the tang so the bottom forms a right angle with the bolster (the part that butts against the barrel where you place your wrench to remove the plug). If your plug has a radius there, it will make the job much harder.
Your tang has a humped sighting groove but TRS did not leave you enough wood on top. You may have to file the edges of the tang down to meet the wood. Here are humped tangs properly installed. These are both hook tangs and breeches but that does not matter. The first 2 show the edges of the tang inlet flush with the wood because there was enough wood above the barrel to allow that.
The next photo shows what you are probably going to have to do, which is file the edges of the tang down to meet the wood. The end result can look just fine as long as the sighting groove doesn't sit up too high.
With respect to your butt plate, you must anneal the wax cast brass before peening. If you don't is may crack because the wax castings can be brittle. Heat to red and then let air cool. You can quench in water but air cooling is a little safer with the wax castings reducing any risk of surface cracking. Use a good heavy ball peen hammer and don't worry about dimpling the surface. That's why you have files.
It looks like your stock is American black walnut, which is a poor cousin compared with the European walnut the stock should be. In my experience, many TRS black walnuts stocks are light and "chippy". As a consequence, you must have your knives and chisels really, really sharp to reduce risk of compressing the wood instead of shearing it off cleanly.
dave